Byzantine Empire, from 12th century

Constantine I (Constantine the Great) established the Eastern Roman Empire in the Greek settlement of Byzantium in 324 CE, henceforth named Constantinople, the present İstanbul. Known as the Byzantine Empire, its symbol had become a double-headed eagle. This symbol dated back to the 12th century and was introduced by the emperors of the Komnenos dynasty. It was based on superstition from Cappadocia about a gigantic eagle with two heads that would steal livestock and kill its owners. Later a sword (“Romfaia”) and the Globe of Orthodoxy were added and the crown by the Palaiologos dynasty. The Greek Orthodox Church, retaining its Byzantine culture, still uses this flag.