17 April

Events
69 – After the First Battle of Bedriacum, Vitellius becomes Roman Emperor.
1080 – King of Denmark Harald III dies and is succeeded by Canute IV, who would later be the first Dane to be canonized.
1397 – Geoffrey Chaucer tells the Canterbury Tales for the first time at the court of Richard II. Chaucer scholars have also identified this date (in 1387) as the start of the book's pilgrimage to Canterbury.
1492 – Spain and Christopher Columbus sign the Capitulations of Santa Fe for his voyage to Asia to acquire spices.
1521 – Trial of Martin Luther over his teachings begins during the assembly of the Diet of Worms. Initially intimidated, he asks for time to reflect before answering and is given a stay of one day.
1524 – Giovanni da Verrazzano reaches New York harbor.
1555 – After 18 months of siege, Siena surrenders to the Florentine-Imperial army. The Republic of Siena is incorporated into the Grand Duchy of Tuscany.
1797 – Sir Ralph Abercromby attacks San Juan, Puerto Rico in what would be one of the largest invasions of the Spanish territories in America.
1797 – Citizens of Verona, Italy, begin an eight-day rebellion against the French occupying forces, which will end unsuccessfully.
1864 – American Civil War: The Battle of Plymouth begins – Confederate forces attack Plymouth, North Carolina.
1895 – The Treaty of Shimonoseki between China and Japan is signed. This marks the end of the First Sino-Japanese War, and the defeated Qing Empire is forced to renounce its claims on Korea and to concede the southern portion of the Fengtien province, Taiwan and the Pescadores Islands to Japan.
1897 – The Aurora, Texas UFO incident
1905 – The Supreme Court of the United States decides Lochner v. New York which holds that the "right to free contract" is implicit in the due process clause of the Fourteenth Amendment of the United States Constitution.
1907 – The Ellis Island immigration center processes 11,747 people, more than on any other day.
1912 – Russian troops open fire on striking goldfield workers in northeast Siberia, killing at least 150.
1941 – World War II: The Kingdom of Yugoslavia surrenders to Germany.
1942 – French prisoner of war General Henri Giraud escapes from his castle prison in Festung Königstein.
1944 – Forces of the Communist-controlled Greek People's Liberation Army attack the smaller National and Social Liberation resistance group, which surrenders. Its leader Dimitrios Psarros is murdered.
1945 – Brazilian forces liberate the town of Montese, Italy, from German Nazi forces.
1946 – Syria obtains its Independence from the French occupation.
1949 – At midnight 26 Irish counties officially leave the British Commonwealth. A 21-gun salute on O'Connell Bridge, Dublin, ushers in the Republic of Ireland.
1951 – The Peak District becomes the United Kingdom's first National Park.
1961 – Bay of Pigs Invasion: A group of CIA financed and trained Cuban exiles lands at the Bay of Pigs in Cuba with the aim of ousting Fidel Castro.
1964 – Jerrie Mock becomes the first woman to circumnavigate the world by air.
1964 – Ford Mustang is introduced to the North American market.
1969 – Sirhan Sirhan is convicted of assassinating Robert F. Kennedy.
1969 – Czechoslovakian Communist Party chairman Alexander Dubček is deposed.
1970 – Apollo program: The ill-fated Apollo 13 spacecraft returns to Earth safely.
1971 – The People's Republic of Bangladesh forms, under Sheikh Mujibur Rahman at Mujibnagor.
1975 – The Cambodian Civil War ends. The Khmer Rouge captures the capital Phnom Penh and Cambodian government forces surrender.
1978 – Mir Akbar Khyber was assassinated, provoking a communist coup d'état in Afghanistan.
1982 – Patriation of the Canadian constitution in Ottawa by Proclamation of Queen Elizabeth II, Queen of Canada.
1984 – Police Constable Yvonne Fletcher is killed by gunfire from the Libyan People's Bureau in London during a small demonstration outside the embassy. Ten others are wounded. The events lead to an 11-day siege of the building.
1986 – The Three Hundred and Thirty Five Years' War between the Netherlands and the Isles of Scilly ends.
2006 – Sami Hammad, a Palestinian suicide bomber, detonates an explosive device in Tel Aviv, killing 11 people and injuring 70.

Holidays and observances

Christian Feast Day:
Blessed Kateri Tekakwitha (Canada)
Pope Anicetus
April 17 (Eastern Orthodox liturgics)
Earliest day on which Store Bededag or General Prayer Day can fall, while May 13 is the latest; observed on the 4th Friday after Easter day. (Denmark)
Evacuation Day, celebrates the recognition of the independence of Syria from France in 1946.
FAO Day (Iraq)
Flag Day (American Samoa)
Women's Day (Gabon)
World Hemophilia Day (International)