caliph
The supreme religious and political authority of Muslims, considered successor of Muhammad (Arabic: khalifa = deputy). He was the head of the Caliphate, the religious state of the Arabs.

Greek fire
Incendiary mixture based on crude oil (‘naphtha’), which was launched with the help of a pressure pump. Its used was spread in Byzantium towards the late 7th century and became one of the most powerful weapons of the Byzantine navy until the invention of canons.

katepano
(from "epano","above") Governor of a katepania. Title that from the end of the 10th century characterized the commanders of large provinces as Italy or Mesopotamia and from the 11th century, it was used also in the regions of Bulgaria, Antioch etc.

monotheletism
Doctrine developed in the 7th century by Patriarch Sergios, who wanted to reconcile the Orthodox with the monophysites of the Byzantine Empire. Monothelitism supported that Jesus had two natures but only one will. Despite the efforts of Emperor Herakleios (610-641) to impose the new doctrine, monothelitism, was renounced as a heresy in 680.

strategos ("general")
During the Roman period his duties were mainly political. Οffice of the Byzantine state´s provincial administration. At first the title was given to the military and political administrator of the themes, namely of the big geographic and administrative unities of the Byzantine empire. Gradually the title lost its power and, already in the 11th century, strategoi were turned to simple commanders of military units, responsible for the defence of a region.