Theodosios' son had been captured by Leo in Nicomedia.

The feeble emperor, realizing that opposition is futile,chooses to resign the throne on March 25, 717.

He and his son subsequently enter the clergy; Theodosios will end his life in a monastery at Ephesus.

Leo now heads an empire humiliated by the presence of pagan barbarians upon Balkan soil rightfully considered “Roman,” threatened by an attack upon its Anatolian heartland and its capital, and reduced, finally, in the West to Sicily and the remnants of the Ravenna exarchate.

Leo's first task is the organization of the defense of Constantinople against eighty thousand Arab troops under Maslama ibn Abd al-Malik, who has angrily perceived his client’s deception.

Approaching Constantinople from Pergamon (Bergama), the Arabs besiege the Roman capital by land and sea from August 15, 717.

Leo's military prowess, augmented by the skillful deployment of Greek fire, forces the invaders from the city walls.

Caliph Sulayman joins the attack with two thousand warships and another eighty thousand troops, but upon landing is driven back by the Roman army.

The caliphate's forces camp for the winter.