One of the most recognisable (other than the cross) and beloved Greek symbols, the double-headed eagle, is not a part of the modern Greek flag or coat of arms (although it is officially used by the Greek Army, the Church of Greece, the Cypriot National Guard and the Church of Cyprus, and was incorporated in the Greek coat of arms between 1925 and 1926). One suggested explanation is that, upon independence, an effort was made for political — and international relations — reasons to limit expressions implying efforts to recreate the Byzantine empire. Yet another theory is that this symbol was only connected with a particular period of Greek history (Byzantine) and a particular form of rule (imperial). More recent research has justified this view, connecting this symbol only to personal and dynastic emblems of Byzantine Emperors.
Greek scholars have attempted to establish links with ancient symbols: the eagle was a common design representing power in ancient city-states, while there was an implication of a "dual-eagle" concept in the tale that Zeus left two eagles fly east and west from the ends of the world, eventually meeting in Delphi, thus proving it to be the centre of the earth. However, there is virtually no doubt that its origin is a blend of Roman and Eastern influences. Indeed, the early Byzantine Empire inherited the Roman eagle as an imperial symbol. During his reign, Emperor Isaac I Comnenus (1057–59) modified it as double-headed, influenced by traditions about such a beast in his native Paphlagonia in Asia Minor (in turn reflecting possibly much older local myths). Many modifications followed in flag details, often combined with the cross. After the recapture of Constantinople by the Byzantine Greeks in 1261, two crowns were added (over each head) representing — according to the most prevalent theory — the newly recaptured capital and the intermediate "capital" of the empire of Nicaea. There has been some confusion about the exact use of this symbol by the Byzantines; it is quite certain that it was a "dynastic" and not a "state" symbol (a term not fully applicable at the time, anyway), and for this reason, the colours connected with it were clearly the colours of "imperial power", i.e., imperial purple and gold.
After the fall of Constantinople to the Ottoman Empire nonetheless, the double-headed eagle remained a strong symbol of reference for the Greeks. Most characteristically, the Orthodox Church continues to use the double-headed eagle extensively as a decorative motif, and has also adopted a black eagle on yellow/gold background as its official flag.
After the Ottoman conquest however this symbol also found its way to a "new Constantinople" (or Third Rome), i.e. Moscow. Russia, deeply influenced by the Byzantine Empire, saw herself as its heir and adopted the double-headed eagle as its imperial symbol. It was also adopted by the Serbs, the Montenegrins, the Albanians and a number of Western rulers, most notably in Germany and Austria.