Byzantine flags and insignia

For most of its history, the Eastern Roman (Byzantine) Empire did not know or use heraldry in the West European sense. Various emblems (Greek: σημεῖα, sēmeia; sing. σημεῖον, sēmeion) were used in official occasions and for military purposes, such as banners or shields displaying various motifs such as the cross or the labarum. The use of the cross, and of icons of Christ, the Theotokos and various saints is also attested on seals of officials, but these were often personal rather than family emblems.

The single-headed Roman imperial eagle continued to be used in Byzantium, although far more rarely. Thus "eagle-bearers" (ὀρνιθόβορας), descendants of the aquilifers of the Roman legions, are still attested in the 6th century military manual known as the Strategikon of Maurice, although it is unknown whether the standards they carried bore any resemblance to the legionary aquilae. On coins, the eagle ceases to appear after the early 7th century, but it is still occasionally found on seals of officials and on stone reliefs. In the last centuries of the Empire it is recorded as being sewn on imperial garments, and shown in illuminated manuscripts as decorating the cushions (suppedia) on which the emperors stood.

The emblem mostly associated with the Byzantine Empire, however, is the double-headed eagle. It is not of Byzantine invention, but a traditional Anatolian motif dating to Hittite times, and the Byzantines themselves only used it in the last centuries of the Empire. The adoption of the double-headed eagle has sometimes been dated to the mid-11th century, when the Komnenoi supposedly adopted it from Hittite rock-carvings in their native Paphlagonia. This, however, is clearly erroneous: although as a decorative motif the double-headed eagle begins to appear in Byzantine art during the 11th century, it is not securely attested in connection with the Emperor and his family until well into the 13th century, under the Palaiologan emperors. Prior to that, in the late 12th and throughout the 13th century, the eagle was used in northern Syria and Upper Mesopotamia: the Artuqid sultans of Amida used it as their insigne, the coins of the Zengid dynasty sported it, and Saladin and the Seljuq sultan Kayqubad I likewise used it as a decorative motif in their buildings.

...
Wikipedia