In 864 Antioch, the capital of the eastern empire, was sacked by the Bulgars and the last Isaurian emperor killed. Theodemar, perceiving that the Bulgar threat was greater than ever before, gathered his army and marched along the coast to Syria. On the 11th June, 865, the Africans won a decisive victory at the Battle of Heliopolis and liberated Antioch three weeks later.
For the next two years he continued to fight the Bulgars and, with the aid of the remnants of the Roman army, managed to push them out of most of Anatolia. When he returned to Antioch he was hailed as a conquering hero and, despite the grumblings of some of the aristocracy who argued he was of barbarian blood, he was acclaimed Emperor by the Senate for being by far the most suitable candidate. Theodemar adopted the Greek name Basil in 867 in an effort to reconcile the complainers to his rule.
As Emperor, Basil was required to convert to Islam and to everybody's surprise he soon became a devout believer. During the latter half of his reign he took steps to introduce the faith to Africa, where it flourished and even became a source of missionaries to the West in its own right. More than anyone else, it is Basil Theodemar who is usually held to be most responsible for the spread of Islam into Western Europe and beyond.
Basil died in 886 and was succeeded by his son, Leo VI.