August 20

AD 14 – Agrippa Postumus, maternal grandson of the late Roman emperor Augustus, is mysteriously executed by his guards while in exile. 636 – Battle of Yarmouk: Arab forces led by Khalid ibn al-Walid take control of the Levant away from the Byzantine Empire, marking the first great wave of Muslim conquests and the rapid advance of Islam outside Arabia. 917 – Battle of Acheloos: Tsar Simeon I of Bulgaria decisively defeats a Byzantine army. 1083 – Canonization of the first King of Hungary, Saint Stephen and his son Saint Emeric celebrated as a National Day in Hungary. 1191 – Richard I of England initiates the Massacre at Ayyadieh, leaving 2,600–3,000 Muslim hostages dead. 1308 – Pope Clement V pardons Jacques de Molay, the last Grand Master of the Knights Templar, absolving him of charges of heresy. 1391 – Konrad von Wallenrode becomes the 24th Grand Master of the Teutonic Order. 1467 – The Second Battle of Olmedo takes places as part of a succession conflict between Henry IV of Castile and his half-brother Alfonso, Prince of Asturias. 1519 – Philosopher and general Wang Yangming defeats Zhu Chenhao, ending the Prince of Ning rebellion against the reign of the Ming dynasty's Zhengde Emperor. 1648 – The Battle of Lens is the last major military confrontation of the Thirty Years' War, contributing to the signing of the Peace of Westphalia in October that year. 1672 – Former Grand Pensionary Johan de Witt and his brother Cornelis are lynched by a mob in The Hague. 1707 – The first Siege of Pensacola comes to an end with the failure of the British to capture Pensacola, Florida. 1710 – War of the Spanish Succession: A multinational army led by the Austrian commander Guido Starhemberg defeats the Spanish-Bourbon army commanded by Alexandre Maître, Marquis de Bay in the Battle of Saragossa. 1775 – The Spanish establish the Presidio San Augustin del Tucson in the town that became Tucson, Arizona. 1794 – Northwest Indian War: United States troops force a confederacy of Shawnee, Mingo, Delaware, Wyandot, Miami, Ottawa, Chippewa, and Potawatomi warriors into a disorganized retreat at the Battle of Fallen Timbers.