In 670 BC, the citizens of Byzantium claimed the crescent moon as their state symbol, after a battle whose victory they attributed to Artemis, the Greek goddess of the hunt. Her symbol was the crescent moon [1]. Nevertheless, Byzantium was the first governing state to use the crescent moon as its national symbol. In 330 AD Constantine I added the Virgin Mary's star to the flag.
The crescent moon and star were not completely abandoned by the Christian world after the fall of Constantinople. To date the official flag of the Orthodox Patriarch of Jerusalem is a lavarum of white, with a church building with two towers, and on either side of the arms, at the top, are the outline in black of a crescent moon facing center, and a star/stars with rays.[1]
http://en.wikipedia.org/wiki/Byzantium