Today:
240: Shapur I is crowned co-emperor of the Sasanian Empire alongside his father, Ardashir I.
1204: The Fourth Crusade captures and begins the sack of Constantinople, marking a major turning point in the decline of the Byzantine Empire.
1606: The Union Jack is adopted by royal decree as the first common flag for the kingdoms of England and Scotland.
1776: North Carolina becomes the first colony to authorize its delegates to vote for independence from Great Britain through the Halifax Resolves.
1861: The American Civil War begins as Confederate forces open fire on Fort Sumter in South Carolina.
1945: United States President Franklin D. Roosevelt dies in office; Vice President Harry S. Truman is sworn in as the 33rd president.
1955: The polio vaccine, developed by Dr. Jonas Salk, is declared safe, effective, and potent for public use.
1961: Soviet cosmonaut Yuri Gagarin becomes the first human to travel into outer space and orbit the Earth aboard Vostok 1.
1981: The first Space Shuttle, Columbia, launches on its maiden orbital mission, marking the start of the NASA Space Shuttle program.
1983: Harold Washington is elected as the first African-American mayor of Chicago.