Year 717 (DCCXVII) was a common year starting on Friday (link will display the full calendar) of the Julian calendar. The denomination 717 for this year has been used since the early medieval period, when the Anno Domini calendar era became the prevalent method in Europe for naming years. Events By place Byzantine Empire March 25 – Emperor Theodosios III is deposed after a reign of 1 year and 10 months. He is succeeded by the 32-year-old Leo III the Isaurian, a general (strategos) of the Anatolic Theme (modern Turkey). Theodosios and his son enter the clergy, and he probably becomes bishop of Ephesus. Leo brings an end to the Twenty Years' Anarchy in the Byzantine Empire, which marks the beginning of the so-called Isaurian Dynasty.Bellinger & Grierson (1992), p. 5 Arab–Byzantine War: Muslim general Maslama ibn Abd al-Malik leads his army of 80,000 men from Pergamum to Abydos, where he crosses the Hellespont. To prevent interference by the Bulgars, or by any Byzantine forces in Thrace, he sends part of his army to a covering position near Adrianople; with his main body, Maslama builds siege lines to blockade Constantinople, which is protected by the massive Theodosian Walls. August 15 – Siege of Constantinople: Maslama begins a combined land and sea effort to capture Constantinople. The capital controls the Bosporus, access between the Mediterranean and Black Sea, and is defended by a garrison of roughly 25,000 men. Leo III orders the granaries be restocked and siege engines installed. The Arab besiegers are suffering immense losses due to disease, and from attrition of siege warfare. September 1 – A Muslim armada, consisting of 1,800 ships commanded by Admiral Suleiman, sails into the Sea of Marmara and drops anchor below the sea walls of Constantinople, to supply their forces ashore. Leo III orders the Byzantine fleet to sally forth from their protected harbors with Greek fire, setting alight the thickly-packed Muslim ships. Many vessels burst into flames, while others collide with each other before sinking. Fall – Basil Onomagoulos, Byzantine official, declares himself rival emperor in Sicily after the news arrives that Constantinople has fallen to an Arab siege. Leo III dispatches a chartoularios named Paul, with imperial instructions for the Byzantine army on the island. Basil is arrested and executed; his head is sent to Leo, while the other rebels are mutilated and exiled. Western Europe March 21 – Battle of