May 20 events in history

325 The First Council of Nicea – the first Ecumenical Council of the Christian Church is held
491 Empress Ariadne marries Anastasius I. The widowed Augusta is able to choose her successor for the Byzantine throne, after Zeno (late emperor) dies of dysentery
526 An earthquake kills about 250,000 people in what is now Syria and Antiochia
685 The Battle of Dun Nechtain is fought between a Pictish army under King Bridei III and the invading Northumbrians under King Ecgfrith, who are decisively defeated
1217 The Second Battle of Lincoln is fought near Lincoln, England, resulting in the defeat of Prince Louis of France by William Marshal, 1st Earl of Pembroke
1293 King Sancho IV of Castile creates the Study of General Schools of Alcalá
1449 The Battle of Alfarrobeira is fought, establishing the House of Braganza as a principal royal family of Portugal
1497 John Cabot sets sail from Bristol, England, on his ship Matthew looking for a route to the west (other documents give a May 2 date)
1498 Portuguese explorer Vasco da Gama discovers the sea route to India when he arrives at Kozhikode (previously known as Calicut), India
1520 The massacre at the festival of Tóxcatl takes place during the Fall of Tenochtitlan, resulting in turning the Aztecs against the Spanish
1521 Ignatius Loyola is seriously wounded in the Battle of Pampeluna
1570 Cartographer Abraham Ortelius issues Theatrum Orbis Terrarum, the first modern atlas
1609 Shakespeare's sonnets are first published in London, perhaps illicitly, by the publisher Thomas Thorpe
1631 The city of Magdeburg in Germany is seized by forces of the Holy Roman Empire and most of its inhabitants massacred, in one of the bloodiest incidents of the Thirty Years' War
1775 Mecklenburg Declaration of Independence is signed in Charlotte, North Carolina
1802 By the Law of 20 May 1802, Napoleon Bonaparte reinstates slavery in the French colonies, revoking its abolition in the French Revolution
1813 Napoleon Bonaparte leads his French troops into the Battle of Bautzen in Saxony, Germany, against the combined armies of Russia and Prussia. The battle ends the next day with a French victory
1840 York Minster is badly damaged by fire
1861 American Civil War: The state of Kentucky proclaims its neutrality, which will last until September 3 when Confederate forces enter the state. Meanwhile, the State of North Carolina secedes from the Union
1862 U.S. President Abraham Lincoln signs the Homestead Act into law
1864 American Civil War: Battle of Ware Bottom Church – in the Virginia Bermuda Hundred Campaign, 10,000 troops fight in this Confederate victory
1873 Levi Strauss and Jacob Davis receive a U.S. patent for blue jeans with copper rivets
1875 Signing of the Metre Convention by 17 nations leading to the establishment of the International System of Units
1882 The Triple Alliance between the German Empire, Austria-Hungary and the Kingdom of Italy is formed
1883 Krakatoa begins to erupt; the volcano explodes three months later, killing more than 36,000 people
1884 Dinuzulu kaCetshwayo becomes the king of the Zulu Nation
1891 History of cinema: The first public display of Thomas Edison's prototype kinetoscope
1896 The six ton chandelier of the Palais Garnier falls on the crowd below resulting in the death of one and the injury of many others
1899 The first traffic ticket in the US: New York City taxi driver Jacob German was arrested for speeding while driving 12 miles per hour on Lexington Street
1902 Cuba gains independence from the United States. Tomás Estrada Palma becomes the country's first President
1908 Budi Utomo organization is founded in Dutch East Indies, beginning the Indonesian National Awakening
1916 The Saturday Evening Post publishes its first cover with a Norman Rockwell painting (Boy with Baby Carriage)
1920 Montreal, Quebec radio station XWA broadcasts the first regularly scheduled radio programming in North America
1927 Treaty of Jeddah: the United Kingdom recognizes the sovereignty of King Ibn Saud in the Kingdoms of Hejaz and Nejd, which later merge to become the Kingdom of Saudi Arabia
1927 At 07:52 Charles Lindbergh takes off from Roosevelt Field in Long Island, New York, on the world's first solo non-stop flight across the Atlantic Ocean. He touched down at Le Bourget Field in Paris at 22:22 the next day
1932 Amelia Earhart takes off from Newfoundland to begin the world's first solo nonstop flight across the Atlantic Ocean by a female pilot, landing in Ireland the next day
1940 The Holocaust: The first prisoners arrive at a new concentration camp at Auschwitz
1941 World War II: Battle of Crete – German paratroops invade Crete
1948 Chiang Kai-shek is elected as the first President of the Republic of China
1949 In the United States, the Armed Forces Security Agency, the predecessor to the National Security Agency, is established
1956 In Operation Redwing, the first United States airborne hydrogen bomb is dropped over Bikini Atoll in the Pacific Ocean
1964 Discovery of the cosmic microwave background radiation by Robert Woodrow Wilson and Arno Penzias
1965 PIA Flight 705, a Pakistan International Airlines Boeing 720-040B, crashes while descending to land at Cairo International Airport, killing 121 of the 127 passengers and crew
1967 The Popular Movement of the Revolution political party is established in the Democratic Republic of the Congo
1968 Operation OAU begins during the Nigerian Civil War
1969 The Battle of Hamburger Hill in Vietnam ends
1980 In a referendum in Quebec, the population rejects by a 60% vote the proposal from its government to move towards independence from Canada
1983 First publications of the discovery of the HIV virus that causes AIDS in the journal Science by Luc Montagnier
1983 Church Street bombing: A car bomb planted by Umkhonto we Sizwe explodes on Church Street in South Africa's capital, Pretoria, killing 19 people and injuring 217 others
1985 Radio Martí, part of the Voice of America service, begins broadcasting to Cuba