On this day in 1931, President Herbert Hoover officially dedicates New York City's Empire State Building, pressing a button from the White House that turns on the building's lights. Hoover's gesture, of course, was symbolic; while the president remained in Washington, D.C., someone else flicked the switches in New York.

The idea for the Empire State Building is said to have been born of a competition between Walter Chrysler of the Chrysler Corporation and John Jakob Raskob of General Motors, to see who could erect the taller building. Chrysler had already begun work on the famous Chrysler Building, the gleaming 1,046-foot skyscraper in midtown Manhattan. Not to be bested, Raskob assembled a group of well-known investors, including former New York Governor Alfred E. Smith. The group chose the architecture firm Shreve, Lamb and Harmon Associates to design the building. The Art-Deco plans, said to have been based in large part on the look of a pencil, were also builder-friendly: The entire building went up in just over a year, under budget (at $40 million) and well ahead of schedule. During certain periods of building, the frame grew an astonishing four-and-a-half stories a week.

At the time of its completion, the Empire State Building, at 102 stories and 1,250 feet high (1,454 feet to the top of the lightning rod), was the world's tallest skyscraper. The Depression-era construction employed as many as 3,400 workers on any single day, most of whom received an excellent pay rate, especially given the economic conditions of the time. The new building imbued New York City with a deep sense of pride, desperately needed in the depths of the Great Depression, when many city residents were unemployed and prospects looked bleak. The grip of the Depression on New York's economy was still evident a year later, however, when only 25 percent of the Empire State's offices had been rented.

In 1972, the Empire State Building lost its title as world's tallest building to New York's World Trade Center, which itself was the tallest skyscraper for but a year. Today the honor belongs to Dubai’s Burj Khalifa tower, which soars 2,717 feet into the sky.

On this day in 1945, holed up in a bunker under his headquarters in Berlin, Adolf Hitler commits suicide by swallowing a cyanide capsule and shooting himself in the head. Soon after, Germany unconditionally surrendered to the Allied forces, ending Hitler's dreams of a "1,000-year" Reich.

Since at least 1943, it was becoming increasingly clear that Germany would fold under the pressure of the Allied forces. In February of that year, the German 6th Army, lured deep into the Soviet Union, was annihilated at the Battle of Stalingrad, and German hopes for a sustained offensive on both fronts evaporated. Then, in June 1944, the Western Allied armies landed at Normandy, France, and began systematically to push the Germans back toward Berlin. By July 1944, several German military commanders acknowledged their imminent defeat and plotted to remove Hitler from power so as to negotiate a more favorable peace. Their attempts to assassinate Hitler failed, however, and in his reprisals, Hitler executed over 4,000 fellow countrymen.

In January 1945, facing a siege of Berlin by the Soviets, Hitler withdrew to his bunker to live out his final days. Located 55 feet under the chancellery, the shelter contained 18 rooms and was fully self-sufficient, with its own water and electrical supply. Though he was growing increasingly mad, Hitler continued to give orders and meet with such close subordinates as Hermann Goering, Heinrich Himmler and Josef Goebbels. He also married his long-time mistress Eva Braun just two days before his suicide.

In his last will and testament, Hitler appointed Admiral Karl Donitz as head of state and Goebbels as chancellor. He then retired to his private quarters with Braun, where he and Braun poisoned themselves and their dogs, before Hitler then also shot himself with his service pistol.

Hitler and Braun's bodies were hastily cremated in the chancellery garden, as Soviet forces closed in on the building. When the Soviets reached the chancellery, they removed Hitler's ashes, continually changing their location so as to prevent Hitler devotees from creating a memorial at his final resting place. Only eight days later, on May 8, 1945, the German forces issued an unconditional surrender, leaving Germany to be carved up by the four Allied powers.

On April 29, 2004, the National World War II Memorial opens in Washington, D.C., to thousands of visitors, providing overdue recognition for the 16 million U.S. men and women who served in the war. The memorial is located on 7.4 acres on the former site of the Rainbow Pool at the National Mall between the Washington Monument and the Lincoln Memorial. The Capitol dome is seen to the east, and Arlington Cemetery is just across the Potomac River to the west.

The granite and bronze monument features fountains between arches symbolizing hostilities in Europe and the Far East. The arches are flanked by semicircles of pillars, one each for the states, territories and the District of Columbia. Beyond the pool is a curved wall of 4,000 gold stars, one for every 100 Americans killed in the war. An Announcement Stone proclaims that the memorial honors those "Americans who took up the struggle during the Second World War and made the sacrifices to perpetuate the gift our forefathers entrusted to us: A nation conceived in liberty and justice."

Though the federal government donated $16 million to the memorial fund, it took more than $164 million in private donations to get it built. Former Kansas Sen. Bob Dole, who was severely wounded in the war, and actor Tom Hanks were among its most vocal supporters. Only a fraction of the 16 million Americans who served in the war would ever see it. Four million World War II veterans were living at the time, with more than 1,100 dying every day, according to government records.

The memorial was inspired by Roger Durbin of Berkey, Ohio, who served under Gen. George S. Patton. At a fish fry near Toledo in February 1987, he asked U.S. Rep. Marcy Kaptur why there was no memorial on the Mall to honor World War II veterans. Kaptur, a Democrat from Ohio, soon introduced legislation to build one, starting a process that would stumble along through 17 years of legislative, legal and artistic entanglements. Durbin died of pancreatic cancer in 2000.

The monument was formally dedicated May 29, 2004, by U.S. President George W. Bush. Open 24 hours a day, seven days a week, it received some 4.4 million visitors in 2005.

On this day in 1945, "Il Duce," Benito Mussolini, and his mistress, Clara Petacci, are shot by Italian partisans who had captured the couple as they attempted to flee to Switzerland.

The 61-year-old deposed former dictator of Italy was established by his German allies as the figurehead of a puppet government in northern Italy during the German occupation toward the close of the war. As the Allies fought their way up the Italian peninsula, defeat of the Axis powers all but certain, Mussolini considered his options. Not wanting to fall into the hands of either the British or the Americans, and knowing that the communist partisans, who had been fighting the remnants of roving Italian fascist soldiers and thugs in the north, would try him as a war criminal, he settled on escape to a neutral country.

He and his mistress made it to the Swiss border, only to discover that the guards had crossed over to the partisan side. Knowing they would not let him pass, he disguised himself in a Luftwaffe coat and helmet, hoping to slip into Austria with some German soldiers. His subterfuge proved incompetent, and he and Petacci were discovered by partisans and shot, their bodies then transported by truck to Milan, where they were hung upside down and displayed publicly for revilement by the masses.

On this day in 4977 B.C., the universe is created, according to German mathematician and astronomer Johannes Kepler, considered a founder of modern science. Kepler is best known for his theories explaining the motion of planets.

Kepler was born on December 27, 1571, in Weil der Stadt, Germany. As a university student, he studied the Polish astronomer Nicolaus Copernicus' theories of planetary ordering. Copernicus (1473-1543) believed that the sun, not the earth, was the center of the solar system, a theory that contradicted the prevailing view of the era that the sun revolved around the earth.

In 1600, Kepler went to Prague to work for Danish astronomer Tycho Brahe, the imperial mathematician to Rudolf II, emperor of the Holy Roman Empire. Kepler's main project was to investigate the orbit of Mars. When Brahe died the following year, Kepler took over his job and inherited Brahe's extensive collection of astronomy data, which had been painstakingly observed by the naked eye. Over the next decade, Kepler learned about the work of Italian physicist and astronomer Galileo Galilei (1564-1642), who had invented a telescope with which he discovered lunar mountains and craters, the largest four satellites of Jupiter and the phases of Venus, among other things. Kepler corresponded with Galileo and eventually obtained a telescope of his own and improved upon the design. In 1609, Kepler published the first two of his three laws of planetary motion, which held that planets move around the sun in ellipses, not circles (as had been widely believed up to that time), and that planets speed up as they approach the sun and slow down as they move away. In 1619, he produced his third law, which used mathematic principles to relate the time a planet takes to orbit the sun to the average distance of the planet from the sun.

Kepler's research was slow to gain widespread traction during his lifetime, but it later served as a key influence on the English mathematician Sir Isaac Newton (1643-1727) and his law of gravitational force. Additionally, Kepler did important work in the fields of optics, including demonstrating how the human eye works, and math. He died on November 15, 1630, in Regensberg, Germany. As for Kepler's calculation about the universe's birthday, scientists in the 20th century developed the Big Bang theory, which showed that his calculations were off by about 13.7 billion years.

On this day in 1954, the Salk polio vaccine field trials, involving 1.8 million children, begin at the Franklin Sherman Elementary School in McLean, Virginia. Children in the United States, Canada and Finland participated in the trials, which used for the first time the now-standard double-blind method, whereby neither the patient nor attending doctor knew if the inoculation was the vaccine or a placebo. On April 12, 1955, researchers announced the vaccine was safe and effective and it quickly became a standard part of childhood immunizations in America. In the ensuing decades, polio vaccines would all but wipe out the highly contagious disease in the Western Hemisphere.

Polio, known officially as poliomyelitis, is an infectious disease that has existed since ancient times and is caused by a virus. It occurs most commonly in children and can result in paralysis. The disease reached epidemic proportions throughout the first half of the 20th century. During the 1940s and 1950s, polio was associated with the iron lung, a large metal tank designed to help polio victims suffering from respiratory paralysis breathe.

President Franklin Roosevelt was diagnosed with polio in 1921 at the age of 39 and was left paralyzed from the waist down and forced to use leg braces and a wheelchair for the rest of his life. In 1938, Roosevelt helped found the National Foundation for Infantile Paralysis, later renamed the March of Dimes. The organization was responsible for funding much of the research concerning the disease, including the Salk vaccine trials.

The man behind the original vaccine was New York-born physician and epidemiologist Jonas Salk (1914-95). Salk's work on an anti-influenza vaccine in the 1940s, while at the University of Michigan School of Public Health, led him, in 1952 at the University of Pittsburgh, to develop the inactivated polio vaccine (IPV), based on a killed-virus strain of the disease. The 1954 field trials that followed, the largest in U.S. history at the time, were led by Salk's former University of Michigan colleague, Dr. Thomas Francis, Jr.

In the late 1950s, Polish-born physician and virologist Albert Sabin (1906-1993) tested an oral polio vaccine (OPV) he had created from a weakened live virus. The vaccine, easier to administer and cheaper to produce than Salk's, became available for use in America in the early 1960s and eventually replaced Salk's as the vaccine of choice in most countries.

Today, polio has been eliminated throughout much of the world due to the vaccine; however, there is still no cure for the disease and it persists in a small number of countries in Africa and Asia.

On this day in 1983, the Soviet Union releases a letter that Russian leader Yuri Andropov wrote to Samantha Smith, an American fifth-grader from Manchester, Maine, inviting her to visit his country. Andropov's letter came in response to a note Smith had sent him in December 1982, asking if the Soviets were planning to start a nuclear war. At the time, the United States and Soviet Union were Cold War enemies.

President Ronald Reagan, a passionate anti-communist, had dubbed the Soviet Union the "evil empire" and called for massive increases in U.S. defense spending to meet the perceived Soviet threat. In his public relations duel with Reagan, known as the "Great Communicator," Andropov, who had succeeded longtime Soviet leader Leonid Brezhnev in 1982, assumed a folksy, almost grandfatherly approach that was incongruous with the negative image most Americans had of the Soviets.

Andropov's letter said that Russian people wanted to "live in peace, to trade and cooperate with all our neighbors on the globe, no matter how close or far away they are, and, certainly, with such a great country as the United States of America." In response to Smith's question about whether the Soviet Union wished to prevent nuclear war, Andropov declared, "Yes, Samantha, we in the Soviet Union are endeavoring and doing everything so that there will be no war between our two countries, so that there will be no war at all on earth." Andropov also complimented Smith, comparing her to the spunky character Becky Thatcher from "The Adventures of Tom Sawyer" by Mark Twain.

Smith, born June 29, 1972, accepted Andropov's invitation and flew to the Soviet Union with her parents for a visit. Afterward, she became an international celebrity and peace ambassador, making speeches, writing a book and even landing a role on an American television series. In February 1984, Yuri Andropov died from kidney failure and was succeeded by Konstantin Chernenko. The following year, in August 1985, Samantha Smith died tragically in a plane crash at age 13. 

On this day in 1916, on Easter Monday in Dublin, the Irish Republican Brotherhood, a secret organization of Irish nationalists led by Patrick Pearse, launches the so-called Easter Rebellion, an armed uprising against British rule. Assisted by militant Irish socialists under James Connolly, Pearse and his fellow Republicans rioted and attacked British provincial government headquarters across Dublin and seized the Irish capital's General Post Office. Following these successes, they proclaimed the independence of Ireland, which had been under the repressive thumb of the United Kingdom for centuries, and by the next morning were in control of much of the city. Later that day, however, British authorities launched a counteroffensive, and by April 29 the uprising had been crushed. Nevertheless, the Easter Rebellion is considered a significant marker on the road to establishing an independent Irish republic.

Following the uprising, Pearse and 14 other nationalist leaders were executed for their participation and held up as martyrs by many in Ireland. There was little love lost among most Irish people for the British, who had enacted a series of harsh anti-Catholic restrictions, the Penal Laws, in the 18th century, and then let 1.5 million Irish starve during the Potato Famine of 1845-1848. Armed protest continued after the Easter Rebellion and in 1921, 26 of Ireland's 32 counties won independence with the declaration of the Irish Free State. The Free State became an independent republic in 1949. However, six northeastern counties of the Emerald Isle remained part of the United Kingdom, prompting some nationalists to reorganize themselves into the Irish Republican Army (IRA) to continue their struggle for full Irish independence.

In the late 1960s, influenced in part by the U.S. civil rights movement, Catholics in Northern Ireland, long discriminated against by British policies that favored Irish Protestants, advocated for justice. Civil unrest broke out between Catholics and Protestants in the region and the violence escalated as the pro-Catholic IRA battled British troops. An ongoing series of terrorist bombings and attacks ensued in a drawn-out conflict that came to be known as "The Troubles." Peace talks eventually took place throughout the mid- to late 1990s, but a permanent end to the violence remained elusive. Finally, in July 2005, the IRA announced its members would give up all their weapons and pursue the group's objectives solely through peaceful means. By the fall of 2006, the Independent Monitoring Commission reported that the IRA's military campaign to end British rule was over.

According to tradition, the great English dramatist and poet William Shakespeare is born in Stratford-on-Avon on April 23, 1564. It is impossible to be certain the exact day on which he was born, but church records show that he was baptized on April 26, and three days was a customary amount of time to wait before baptizing a newborn. Shakespeare's date of death is conclusively known, however: it was April 23, 1616. He was 52 years old and had retired to Stratford three years before.

Although few plays have been performed or analyzed as extensively as the 38 plays ascribed to William Shakespeare, there are few surviving details about the playwright's life. This dearth of biographical information is due primarily to his station in life; he was not a noble, but the son of John Shakespeare, a leather trader and the town bailiff. The events of William Shakespeare's early life can only be gleaned from official records, such as baptism and marriage records.

He probably attended the grammar school in Stratford, where he would have studied Latin and read classical literature. He did not go to university but at age 18 married Anne Hathaway, who was eight years his senior and pregnant at the time of the marriage. Their first daughter, Susanna, was born six months later, and in 1585 William and Anne had twins, Hamnet and Judith. Hamnet, Shakespeare's only son, died 11 years later, and Anne Shakespeare outlived her husband, dying in 1623. Nothing is known of the period between the birth of the twins and Shakespeare's emergence as a playwright in London in the early 1590s, but unfounded stories have him stealing deer, joining a group of traveling players, becoming a schoolteacher, or serving as a soldier in the Low Countries.

The first reference to Shakespeare as a London playwright came in 1592, when a fellow dramatist, Robert Greene, wrote derogatorily of him on his deathbed. It is believed that Shakespeare had written the three parts of Henry VI by that point. In 1593, Venus and Adonis was Shakespeare's first published poem, and he dedicated it to the young Henry Wriothesley, the 3rd earl of Southampton. In 1594, having probably composed, among other plays, Richard III, The Comedy of Errors, and The Taming of the Shrew, he became an actor and playwright for the Lord Chamberlain's Men, which became the King's Men after James I's ascension in 1603. The company grew into England's finest, in no small part because of Shakespeare, who was its principal dramatist. It also had the finest actor of the day, Richard Burbage, and the best theater, the Globe, which was located on the Thames' south bank. Shakespeare stayed with the King's Men until his retirement and often acted in small parts.

By 1596, the company had performed the classic Shakespeare plays Romeo and Juliet, Richard II, and A Midsummer Night's Dream. That year, John Shakespeare was granted a coat of arms, a testament to his son's growing wealth and fame. In 1597, William Shakespeare bought a large house in Stratford. In 1599, after producing his great historical series, the first and second part of Henry IV and Henry V, he became a partner in the ownership of the Globe Theatre.

The beginning of the 17th century saw the performance of the first of his great tragedies, Hamlet. The next play, The Merry Wives of Windsor, was written at the request of Queen Elizabeth I, who wanted to see another play that included the popular character Falstaff. During the next decade, Shakespeare produced such masterpieces as Othello, King Lear, Macbeth, and The Tempest. In 1609, his sonnets, probably written during the 1590s, were published. The 154 sonnets are marked by the recurring themes of the mutability of beauty and the transcendent power of love and art.

Shakespeare died in Stratford-on-Avon on April 23, 1616. Today, nearly 400 years later, his plays are performed and read more often and in more nations than ever before. In a million words written over 20 years, he captured the full range of human emotions and conflicts with a precision that remains sharp today. As his great contemporary the poet and dramatist Ben Jonson said, "He was not of an age, but for all time."

Earth Day, an event to increase public awareness of the world's environmental problems, is celebrated in the United States for the first time. Millions of Americans, including students from thousands of colleges and universities, participated in rallies, marches, and educational programs.

Earth Day was the brainchild of Senator Gaylord Nelson of Wisconsin, a staunch environmentalist who hoped to provide unity to the grassroots environmental movement and increase ecological awareness. "The objective was to get a nationwide demonstration of concern for the environment so large that it would shake the political establishment out of its lethargy," Senator Nelson said, "and, finally, force this issue permanently onto the national political agenda." Earth Day indeed increased environmental awareness in America, and in July of that year the Environmental Protection Agency was established by special executive order to regulate and enforce national pollution legislation.

On April 22, 1990, the 20th anniversary of Earth Day, more than 200 million people in 141 countries participated in Earth Day celebrations.

Earth Day has been celebrated on different days by different groups internationally. The United Nations officially celebrates it on the vernal equinox, which usually occurs about March 21.

According to tradition, on April 21, 753 B.C., Romulus and his twin brother, Remus, found Rome on the site where they were suckled by a she-wolf as orphaned infants. Actually, the Romulus and Remus myth originated sometime in the fourth century B.C., and the exact date of Rome's founding was set by the Roman scholar Marcus Terentius Varro in the first century B.C.

According to the legend, Romulus and Remus were the sons of Rhea Silvia, the daughter of King Numitor of Alba Longa. Alba Longa was a mythical city located in the Alban Hills southeast of what would become Rome. Before the birth of the twins, Numitor was deposed by his younger brother Amulius, who forced Rhea to become a vestal virgin so that she would not give birth to rival claimants to his title. However, Rhea was impregnated by the war god Mars and gave birth to Romulus and Remus. Amulius ordered the infants drowned in the Tiber, but they survived and washed ashore at the foot of the Palatine hill, where they were suckled by a she-wolf until they were found by the shepherd Faustulus.

Reared by Faustulus and his wife, the twins later became leaders of a band of young shepherd warriors. After learning their true identity, they attacked Alba Longa, killed the wicked Amulius, and restored their grandfather to the throne. The twins then decided to found a town on the site where they had been saved as infants. They soon became involved in a petty quarrel, however, and Remus was slain by his brother. Romulus then became ruler of the settlement, which was named "Rome" after him.

To populate his town, Romulus offered asylum to fugitives and exiles. Rome lacked women, however, so Romulus invited the neighboring Sabines to a festival and abducted their women. A war then ensued, but the Sabine women intervened to prevent the Sabine men from seizing Rome. A peace treaty was drawn up, and the communities merged under the joint rule of Romulus and the Sabine king, Titus Tatius. Tatius' early death, perhaps perpetrated by Romulus, left the Roman as the sole king again. After a long and successful rule, Romulus died under obscure circumstances. Many Romans believed he was changed into a god and worshipped him as the deity Quirinus. After Romulus, there were six more kings of Rome, the last three believed to be Etruscans. Around 509 B.C., the Roman republic was established.

Another Roman foundation legend, which has its origins in ancient Greece, tells of how the mythical Trojan Aeneas founded Lavinium and started a dynasty that would lead to the birth of Romulus and Remus several centuries later. In the Iliad, an epic Greek poem probably composed by Homer in the eighth century B.C., Aeneas was the only major Trojan hero to survive the Greek destruction of Troy. A passage told of how he and his descendants would rule the Trojans, but since there was no record of any such dynasty in Troy, Greek scholars proposed that Aeneas and his followers relocated.

In the fifth century B.C., a few Greek historians speculated that Aeneas settled at Rome, which was then still a small city-state. In the fourth century B.C., Rome began to expand within the Italian peninsula, and Romans, coming into greater contact with the Greeks, embraced the suggestion that Aeneas had a role in the foundation of their great city. In the first century B.C., the Roman poet Virgil developed the Aeneas myth in his epic poem the Aeneid, which told of Aeneas' journey to Rome. Augustus, the first Roman emperor and emperor during Virgil's time, and Julius Caesar, his great-uncle and predecessor as Roman ruler, were said to be descended from Aeneas.

On April 20, 1980, the Castro regime announces that all Cubans wishing to emigrate to the U.S. are free to board boats at the port of Mariel west of Havana, launching the Mariel Boatlift. The first of 125,000 Cuban refugees from Mariel reached Florida the next day.

The boatlift was precipitated by housing and job shortages caused by the ailing Cuban economy, leading to simmering internal tensions on the island. On April 1, Hector Sanyustiz and four others drove a bus through a fence at the Peruvian embassy and were granted political asylum. Cuban guards on the street opened fire. One guard was killed in the crossfire.

The Cuban government demanded the five be returned for trial in the dead guard's death. But when the Peruvian government refused, Castro withdrew his guards from the embassy on Good Friday, April 4. By Easter Sunday, April 6, some 10,000 Cubans crowded into the lushly landscaped gardens at the embassy requesting asylum. Other embassies, including those of Spain and Costa Rica, agreed to take a small number of people. But suddenly, two weeks later, Castro proclaimed that the port of Mariel would be opened to anyone wishing to leave, as long as they had someone to pick them up. Cuban exiles in the United States rushed to hire boats in Miami and Key West and rescue their relatives.

In all, 125,000 Cubans fled to U.S. shores in about 1,700 boats, creating large waves of people that overwhelmed the U.S. Coast guard. Cuban guards had packed boat after boat, without considering safety, making some of the overcrowded boats barely seaworthy. Twenty-seven migrants died, including 14 on an overloaded boat that capsized on May 17.

The boatlift also began to have negative political implications for U.S. President Jimmy Carter. When it was discovered that a number of the exiles had been released from Cuban jails and mental health facilities, many were placed in refugee camps while others were held in federal prisons to undergo deportation hearings. Of the 125,000 "Marielitos," as the refugees came to be known, who landed in Florida, more than 1,700 were jailed and another 587 were detained until they could find sponsors.

The exodus was finally ended by mutual agreement between the U.S. and Cuban governments in October 1980.

On April 19, 1897, John J. McDermott of New York won the first Boston Marathon with a time of 2:55:10.

The Boston Marathon was the brainchild of Boston Athletic Association member and inaugural U.S. Olympic team manager John Graham, who was inspired by the marathon at the first modern Olympic Games in Athens in 1896. With the assistance of Boston businessman Herbert H. Holton, various routes were considered, before a measured distance of 24.5 miles from the Irvington Oval in Boston to Metcalf's Mill in Ashland was eventually selected.

Fifteen runners started the race but only 10 made it to the finish line. John J. McDermott, representing the Pastime Athletic Club of New York City, took the lead from Harvard athlete Dick Grant over the hills in Newton. Although he walked several times during the final miles, McDermott still won by a comfortable six-minute, fifty-two-seconds. McDermott had won the only other marathon on U.S. soil the previous October in New York.

The marathon's distance was changed in 1908 in accordance with Olympic standards to its current length of 26 miles 385 yards.

The Boston Marathon was originally held on Patriot's Day, April 19, a regional holiday that commemorates the beginning of the Revolutionary War. In years when the 19th fell on a Sunday, the race was held the following Monday. In 1969, Patriots Day was officially moved to the third Monday in April and the race has been held on that Monday ever since.

Women were not allowed to enter the Boston race officially until 1972, but Roberta "Bobbi" Gibb couldn't wait: In 1966, she became the first woman to run the entire Boston Marathon, but had to hide in the bushes near the start until the race began. In 1967, Kathrine Switzer, who had registered as "K. V. Switzer", was the first woman to run with a race number. Switzer finished even though officials tried to physically remove her from the race after she was identified as a woman.

In the fall of 1971, the Amateur Athletics Union permitted its sanctioned marathons (including Boston) to allow female entry. Nina Kuscsik became the first official female participant to win the Boston Marathon in 1972. Seven other women started and finished that race.

In 1975, the Boston Marathon became the first major marathon to include a wheelchair division competition. Bob Hall won it in two hours, 58 minutes.

At 5:13 a.m., an earthquake estimated at close to 8.0 on the Richter scale strikes San Francisco, California, killing hundreds of people as it topples numerous buildings. The quake was caused by a slip of the San Andreas Fault over a segment about 275 miles long, and shock waves could be felt from southern Oregon down to Los Angeles.

San Francisco's brick buildings and wooden Victorian structures were especially devastated. Fires immediately broke out and--because broken water mains prevented firefighters from stopping them--firestorms soon developed citywide. At 7 a.m., U.S. Army troops from Fort Mason reported to the Hall of Justice, and San Francisco Mayor E.E. Schmitz called for the enforcement of a dusk-to-dawn curfew and authorized soldiers to shoot-to-kill anyone found looting. Meanwhile, in the face of significant aftershocks, firefighters and U.S. troops fought desperately to control the ongoing fire, often dynamiting whole city blocks to create firewalls. On April 20, 20,000 refugees trapped by the massive fire were evacuated from the foot of Van Ness Avenue onto the USS Chicago.

By April 23, most fires were extinguished, and authorities commenced the task of rebuilding the devastated metropolis. It was estimated that some 3,000 people died as a result of the Great San Francisco Earthquake and the devastating fires it inflicted upon the city. Almost 30,000 buildings were destroyed, including most of the city's homes and nearly all the central business district.

With the world anxiously watching, Apollo 13, a U.S. lunar spacecraft that suffered a severe malfunction on its journey to the moon, safely returns to Earth.

On April 11, the third manned lunar landing mission was launched from Cape Canaveral, Florida, carrying astronauts James A. Lovell, John L. Swigert, and Fred W. Haise. The mission was headed for a landing on the Fra Mauro highlands of the moon. However, two days into the mission, disaster struck 200,000 miles from Earth when oxygen tank No. 2 blew up in the spacecraft. Swigert reported to mission control on Earth, "Houston, we've had a problem here," and it was discovered that the normal supply of oxygen, electricity, light, and water had been disrupted. The landing mission was aborted, and the astronauts and controllers on Earth scrambled to come up with emergency procedures. The crippled spacecraft continued to the moon, circled it, and began a long, cold journey back to Earth.

The astronauts and mission control were faced with enormous logistical problems in stabilizing the spacecraft and its air supply, as well as providing enough energy to the damaged fuel cells to allow successful reentry into Earth's atmosphere. Navigation was another problem, and Apollo 13's course was repeatedly corrected with dramatic and untested maneuvers. On April 17, tragedy turned to triumph as the Apollo 13 astronauts touched down safely in the Pacific Ocean.

In Basel, Switzerland, Albert Hoffman, a Swiss chemist working at the Sandoz pharmaceutical research laboratory, accidentally consumes LSD-25, a synthetic drug he had created in 1938 as part of his research into the medicinal value of lysergic acid compounds. After taking the drug, formally known as lysergic acid diethylamide, Dr. Hoffman was disturbed by unusual sensations and hallucinations. In his notes, he related the experience:

"Last Friday, April 16, 1943, I was forced to interrupt my work in the laboratory in the middle of the afternoon and proceed home, being affected by a remarkable restlessness, combined with a slight dizziness. At home I lay down and sank into a not unpleasant, intoxicated-like condition characterized by an extremely stimulated imagination. In a dreamlike state, with eyes closed (I found the daylight to be unpleasantly glaring), I perceived an uninterrupted stream of fantastic pictures, extraordinary shapes with intense, kaleidoscopic play of colors. After some two hours this condition faded away."

After intentionally taking the drug again to confirm that it had caused this strange physical and mental state, Dr. Hoffman published a report announcing his discovery, and so LSD made its entry into the world as a hallucinogenic drug. Widespread use of the so-called "mind-expanding" drug did not begin until the 1960s, when counterculture figures such as Albert M. Hubbard, Timothy Leary, and Ken Kesey publicly expounded on the benefits of using LSD as a recreational drug. The manufacture, sale, possession, and use of LSD, known to cause negative reactions in some of those who take it, were made illegal in the United States in 1965.

On this day in 1947, Jackie Robinson, age 28, becomes the first African-American player in Major League Baseball when he steps onto Ebbets Field in Brooklyn to compete for the Brooklyn Dodgers. Robinson broke the color barrier in a sport that had been segregated for more than 50 years. Exactly 50 years later, on April 15, 1997, Robinson's groundbreaking career was honored and his uniform number, 42, was retired from Major League Baseball by Commissioner Bud Selig in a ceremony attended by over 50,000 fans at New York City's Shea Stadium. Robinson's was the first-ever number retired by all teams in the league.

Jack Roosevelt Robinson was born January 31, 1919, in Cairo, Georgia, to a family of sharecroppers. Growing up, he excelled at sports and attended the University of California at Los Angeles, where he was the first athlete to letter in four varsity sports: baseball, basketball, football and track. After financial difficulties forced Robinson to drop out of UCLA, he joined the army in 1942 and was commissioned as a second lieutenant. After protesting instances of racial discrimination during his military service, Robinson was court-martialed in 1944. Ultimately, though, he was honorably discharged.

After the army, Robinson played for a season in the Negro American League. In 1945, Branch Rickey, general manager of the Brooklyn Dodgers, recruited Robinson, who was known for his integrity and intelligence as well as his talent, to join one of the club's farm teams. In 1947, Robinson was called up to the Majors and soon became a star infielder and outfielder for the Dodgers, as well as the National League's Rookie of the Year. In 1949, the right-hander was named the National League's Most Valuable Player and league batting champ. Robinson played on the National League All-Star team from 1949 through 1954 and led the Dodgers to six National League pennants and one World Series, in 1955. He was inducted into the Baseball Hall of Fame in 1962, his first year of eligibility.

Despite his talent and success as a player, Robinson faced tremendous racial discrimination throughout his career, from baseball fans and some fellow players. Additionally, Jim Crow laws prevented Robinson from using the same hotels and restaurants as his teammates while playing in the South.

After retiring from baseball in 1957, Robinson became a businessman and civil rights activist. He died October 24, 1972, at age 53, in Stamford, Connecticut.

On this day in 1865, John Wilkes Booth, an actor and Confederate sympathizer, fatally shoots President Abraham Lincoln at a play at Ford's Theater in Washington, D.C.  The attack came only five days after Confederate General Robert E. Lee surrendered his massive army at Appomattox Court House, Virginia, effectively ending the American Civil War.

Booth, a Maryland native born in 1838, who remained in the North during the war despite his Confederate sympathies, initially plotted to capture President Lincoln and take him to Richmond, the Confederate capital. However, on March 20, 1865, the day of the planned kidnapping, the president failed to appear at the spot where Booth and his six fellow conspirators lay in wait. Two weeks later, Richmond fell to Union forces.

In April, with Confederate armies near collapse across the South, Booth hatched a desperate plan to save the Confederacy. Learning that Lincoln was to attend a performance of "Our American Cousin" at Ford's Theater on April 14, Booth masterminded the simultaneous assassination of Lincoln, Vice President Andrew Johnson and Secretary of State William H. Seward. By murdering the president and two of his possible successors, Booth and his conspirators hoped to throw the U.S. government into disarray.

On the evening of April 14, conspirator Lewis T. Powell burst into Secretary of State Seward's home, seriously wounding him and three others, while George A. Atzerodt, assigned to Vice President Johnson, lost his nerve and fled. Meanwhile, just after 10 p.m., Booth entered Lincoln's private theater box unnoticed and shot the president with a single bullet in the back of his head. Slashing an army officer who rushed at him, Booth leapt to the stage and shouted "Sic semper tyrannis! [Thus always to tyrants]–the South is avenged!" Although Booth broke his leg jumping from Lincoln's box, he managed to escape Washington on horseback.

The president, mortally wounded, was carried to a lodging house opposite Ford's Theater. About 7:22 a.m. the next morning, Lincoln, age 56, died–the first U.S. president to be assassinated. Booth, pursued by the army and other secret forces, was finally cornered in a barn near Bowling Green, Virginia, and died from a possibly self-inflicted bullet wound as the barn was burned to the ground. Of the eight other people eventually charged with the conspiracy, four were hanged and four were jailed. Lincoln, the 16th U.S. president, was buried on May 4, 1865, in Springfield, Illinois.

On this day in 1997, 21-year-old Tiger Woods wins the prestigious Masters Tournament by a record 12 strokes in Augusta, Georgia. It was Woods' first victory in one of golf's four major championships–the U.S. Open, the British Open, the PGA Championship, and the Masters–and the greatest performance by a professional golfer in more than a century.

Eldrick "Tiger" Woods was born in a suburb of Los Angeles, California, on December 30, 1975. The only child of an African-American father and a Thai mother, Woods was encouraged from infancy by his father for a career in golf. At the age of two, he teed off against comedian Bob Hope on television's Mike Douglas Show. At five years old, he was featured on the television show That's Incredible. At age eight, Tiger won his first junior world championship, and in 1991, at age 15, he became the youngest player ever to win the U.S. Junior Amateur Championship. He also captured the 1992 and 1993 Junior Amateur titles, and in 1994 accepted a scholarship to attend Stanford University. That year, he came from six holes behind to win the first of his three consecutive U.S. Amateur championships. He was 18 years old and the youngest Amateur champion in history.

In 1995, Tiger played the Masters, his first professional major championship. The Augusta National Golf Club, which runs the Masters, had not let an African-American join its ranks until 1991. Woods finished 41st in his first Masters appearance. In 1996, he won the collegiate title. By this time, he was already attracting considerable media attention and attracting throngs of new fans to the sport. After claiming his third U.S. Amateur title, Woods left college and turned professional in August 1996. Playing as a pro in eight Professional Golfers' Association (PGA) events in 1996, he won a title and was named the PGA Tour's outstanding rookie. In December 1996, he was celebrated by the magazine Sports Illustrated as its "Sportsman of the Year."

In professional play, most of Woods' opponents were in their late 30s or early 40s. At 6'2" and 155 pounds, he was slender and athletic, and had developed a devastating swing that routinely allowed him to hit drives of more than 300 yards. He also had a reputation for mental toughness and was a superb putter and chipper. In April 1997, all these attributes came together for the most decisive victory in the Masters' 44-year history.

His margin of victory–12 strokes–was the largest in the 20th century, and second only to Old Tom Morris' 13-shot margin at the 1862 British Open. His score of 18-under-par 270 broke Jack Nicklaus' 32-year-old Masters record of 17-under-par 271. He was the youngest golfer by two years to win the Masters and the first person of Asian or African heritage to win a major. Never before had so many spectators come to Augusta National, and never before had so many people watched it on television.

By June 1997, Tiger was ranked number one in the world. In 1999, he won eight PGA tournaments, earned a record $6 million, and began a winning streak that eventually tied Ben Hogan's 1948 streak, the second longest in PGA history. In June 2000, he won his first U.S. Open title, shooting a record 12-under-par 272 to finish 15 strokes ahead of his nearest competitors. It was the greatest professional golf performance in history, surpassing even his 1997 Masters' triumph and Old Tom Morris' 1862 showing. In July 2000, he captured the British Open, and in August the PGA championship. At the age of 24, he was the youngest player ever to win all four major golf titles and just the second to win three majors in a year. On April 10, 2005, he earned his fourth green sport coat at Augusta National, becoming the first person to win four Masters before age 30.

Tiger’s winning pace slowed around 2004, when he devoted time to reworking his swing and rehabilitating his surgically repaired knee. It was also during this period that he married Elin Nordegren, a Swedish former model who would become the mother of his two children. Tiger was back in top form by 2005, winning his 10th major. His performance fluctuated throughout the rest of the decade as he struggled with a torn ACL and personal problems that garnered substantial media attention: In late 2009, in the wake of events surrounding a car accident outside Tiger’s Florida home, several women came forward claiming to have had affairs with the famous golfer. Nordegren divorced him in August 2010, just as Tiger began his first winless season in his career.

The bloodiest four years in American history begin when Confederate shore batteries under General P.G.T. Beauregard open fire on Union-held Fort Sumter in South Carolina's Charleston Bay. During the next 34 hours, 50 Confederate guns and mortars launched more than 4,000 rounds at the poorly supplied fort. On April 13, U.S. Major Robert Anderson surrendered the fort. Two days later, U.S. President Abraham Lincoln issued a proclamation calling for 75,000 volunteer soldiers to quell the Southern "insurrection."

As early as 1858, the ongoing conflict between North and South over the issue of slavery had led Southern leadership to discuss a unified separation from the United States. By 1860, the majority of the slave states were publicly threatening secession if the Republicans, the anti-slavery party, won the presidency. Following Republican Abraham Lincoln's victory over the divided Democratic Party in November 1860, South Carolina immediately initiated secession proceedings. On December 20, the South Carolina legislature passed the "Ordinance of Secession," which declared that "the Union now subsisting between South Carolina and other states, under the name of the United States of America, is hereby dissolved." After the declaration, South Carolina set about seizing forts, arsenals, and other strategic locations within the state. Within six weeks, five more Southern states--Mississippi, Florida, Alabama, Georgia, and Louisiana--had followed South Carolina's lead.

In February 1861, delegates from those states convened to establish a unified government. Jefferson Davis of Mississippi was subsequently elected the first president of the Confederate States of America. When Abraham Lincoln was inaugurated on March 4, 1861, a total of seven states (Texas had joined the pack) had seceded from the Union, and federal troops held only Fort Sumter in South Carolina, Fort Pickens off the Florida coast, and a handful of minor outposts in the South. Four years after the Confederate attack on Fort Sumter, the Confederacy was defeated at the total cost of 620,000 Union and Confederate soldiers dead.