Today

1775 - The American Revolution begins when a "shot heard around the world" is fired in Lexington, Mass.

1861 - The first blood of the American Civil War is shed when a secessionist mob in Baltimore attacks Massachusetts troops bound for Washington, D.C. Four soldiers and 12 rioters are killed.

1994 - A massive explosion at the Alfred P. Murrah Federal Building in Oklahoma City kills 168 people and injures hundreds more.

Tomorrow

1871 - With passage of the Third Force Act, popularly known as the Ku Klux Klan Act, Congress authorizes President Ulysses Grant to declare martial law, impose heavy penalties against terrorist organizations and use military force to suppress the Ku Klux Klan.

1902 - Marie and Pierre Curie successfully isolate radioactive radium salts from the mineral pitchblende in their laboratory in Paris.

1999 - Two teenage gunmen kill 13 people in a shooting spree at Columbine High School in Littleton, Colo.

Wednesday

1955 - Bob Hope's long-running radio program airs for the last time.

1956 - "Heartbreak Hotel" hits the top of the Billboard charts. The song was Elvis' first No. 1 hit.

1989 - One hundred thousand Chinese students begin protests at Tiananmen Square.

Thursday

1915 - German forces shock Allied soldiers along the western front by using more than 150 tons of lethal chlorine gas, devastating the Allied line in the first major gas attack by the German army.

1937 - Jack Nicholson is born.

1954 - Sen. Joseph McCarthy begins hearings investigating the Army, which he charges with being "soft" on communism.

Friday

1014 - Brian Boru, the high king of Ireland, is assassinated by a group of retreating Norsemen shortly after his Irish forces defeated them.

1564 - The English dramatist and poet William Shakespeare is born in Stratford-on-Avon.

1975 - At a speech at Tulane University, President Gerald Ford says the Vietnam War is finished as far as America is concerned: "Today, Americans can regain the sense of pride that existed before Vietnam. But it cannot be achieved by re-fighting a war ..."