📅 Today in HistoryMay 21

Roman Emperors Diocletian and Maximian appoint Galerius as Caesar to Diocletian, beginning the period of four rulers known as the Tetrarchy.

Syracuse, Sicily, is captured by the Muslim Aghlabids after a nine-month siege.

Pope John VIII gives blessings to Branimir of Croatia and to the Croatian people, considered to be international recognition of the Croatian state.

Sixteen-year-old Otto III is crowned Holy Roman Emperor.

Dušan's Code, the constitution of the Serbian Empire, is enacted by Dušan the Mighty.

Henry III of Castile sends Ruy González de Clavijo as ambassador to Timur to discuss the possibility of an alliance between Timur and Castile against the Ottoman Empire.

Queen Mary I grants a royal charter to Derby School, as a grammar school for boys in Derby, England.

In the Concert of The Hague, the Dutch Republic, the Commonwealth of England and the Kingdom of France set out their views on how the Second Northern War should end.

The Battle of Long Sault concludes after five days in which French colonial militia, with their Huron and Algonquin allies, are defeated by the Iroquois Confederacy.

The nobility elect John Sobieski King of Poland and Grand Duke of Lithuania.