Byzantine flags and insignia
For most of its history, the Eastern Roman Empire did not use heraldry in the Western European sense of permanent motifs transmitted through hereditary right. Various large aristocratic families employed certain symbols to identify themselves; 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.
Likewise, various emblems were used in official occasions and for military purposes, such as banners or shields displaying various motifs such as the cross or the labarum. Despite the abundance of pre-heraldic symbols in Byzantine society from the 10th century, only through contact with the Crusaders in the 12th century, and particularly following the Fourth Crusade and the establishment of Frankish principalities on Byzantine soil from 1204 onwards, did heraldic uses penetrate in Byzantium. A native Byzantine heraldry began to appear in the middle and lower rungs of aristocratic families in the 14th century, coinciding with the decline of imperial authority and with the fragmentation of political power under the late Palaiologan emperors. However, it never achieved the breadth of adoption, or the systematization, of its Western analogues.
Imperial insignia
Single-headed eagle
The single-headed Roman imperial eagle continued to be used in Byzantium, although far more rarely. Thus "eagle-bearers", 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. Eagle-topped scepters were a frequent feature of consular diptychs, and appear on coins until the reign of Philippikos Bardanes. It continued in use in bas-reliefs in churches and funerary monuments until well into the 11th century, however. 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 on which the emperors stood.Double-headed eagle
The emblem mostly associated with the Byzantine Empire is the double-headed eagle. It is of Byzantine invention and the Byzantines themselves used for over 300 years, the last centuries of the Empire. The date of its adoption by the Byzantines has been hotly debated by scholars.In 1861, the Greek scholar Georgios Chrysovergis wrote that it was adopted by the Komnenoi in 1048. Although this was based on no evidence whatsoever, this view gained wide acceptance and circulation. More careful examination of the primary sources by Spyridon Lambros and August Heisenberg demonstrated that although as a decorative motif the double-headed eagle begins to appear in Byzantine art during the 10th/11th century, it is not securely attested in connection with the emperor until the chrysobull of Andronikos II Palaiologos in 1301, where he is shown on a decorated with the device. Lambros suggested that it was adopted from Hittite rock-carvings, while A. Soloviev argued in favour of a late adoption around 1288, as a talisman against the first Ottoman successes in Anatolia, as a symbolic gesture reaffirming Byzantine rule over both European and Asian territories.
The Palaiologan emperors used the double-headed eagle as a symbol of the senior members of the imperial family. It was mostly used on clothes and other accoutrements, as codified in the mid-14th century by pseudo-Kodinos in his Book of Offices. According to Kodinos, the emperor bore special boots with eagles made of pearls on both shins and on the instep; the Despots wore similar boots of white and purple, and featured pearl-embroidered eagles on their saddles, while the saddle cloth and their tents were white decorated with red eagles. Similarly, the wore blue boots with golden wire-embroidered eagles on a red background, while his saddle cloth was blue with four red embroidered eagles. The only occasion the double-headed eagle appears on a flag is on the ship that bore Emperor John VIII Palaiologos to the Council of Florence, as mentioned by Sphrantzes and confirmed by its depiction in the Filarete Doors of St. Peter's Basilica. According to a handful of surviving examples, such as the supposed "Flag of Andronikos II Palaiologos" in the Vatopedi Monastery, or a frontispiece of a Bible belonging to Demetrios Palaiologos, the Byzantine double-headed eagle was golden on a red background. Likewise, in Western armorials from the 15th century, the golden double-headed eagle on a red shield is given as the arms of the "Empire of the East" or "of Constantinople", or as emblem of members of the imperial family. The representation of the eagle on a shield is an adaptation to Western heraldic practice, however; the Byzantines never used it in this manner for themselves, although they employed it in a Western context, e.g. in the award of the right to bear the imperial arms to the Florentine citizen Giacomo Paolo di Morellis in 1439. Western European rulers in Greek lands, like Esau de' Buondelmonti and Carlo I Tocco, also impaled their arms with the double-headed eagle as a sign of their status when they received the title of despot from the Byzantine emperors.
Within the Byzantine world, the eagle was also used by the semi-autonomous Despots of the Morea, who were younger imperial princes, and by the Gattilusi of Lesbos, who were Palaiologan relatives and vassals. The double-headed eagle was used in the breakaway Empire of Trebizond as well, being attested imperial clothes but also on flags. Indeed, Western portolans of the 14th–15th centuries use the double-headed eagle as the symbol of Trebizond rather than Constantinople. Single-headed eagles are also attested in Trapezuntine coins, and a 1421 source depicts the Trapezuntine flag as yellow with a red single-headed eagle. Apparently, just as in the metropolitan Byzantine state, the use of both motifs, single and double-headed, continued side by side. Double-headed eagle reliefs are also attested for the walls of Trebizond, with one example preserved in a church in Kalamaria, Thessaloniki, which is very similar to 13th-century Seljuq examples. Modern scholars commonly consider the double-headed eagle to have been adopted by the Grand Komnenos emperors of Trebizond after their recognition of the suzerainty of, and intermarriage with, the Palaiologos dynasty in the 1280s. Likewise, the small Byzantine Principality of Theodoro in the Crimean Peninsula, whose rulers conducted marriage alliances with both the Palaiologoi and the Grand Komnenoi, also used the double-headed eagle in the 15th century.
Other Balkan states copied the Byzantine model: chiefly the Serbians, but also the Bulgarians and Epirus under George Kastrioti, while after 1472 the eagle was adopted by Muscovy and then Russia. In Western Europe, the Holy Roman Empire likewise adopted the double-headed eagle in the mid-13th century, under Frederick II Hohenstaufen, and used it side by side with the single-headed version. In addition, the double-headed eagle may have been in use in the Latin Empire established after the Fourth Crusade: according to Robert of Clari, the first Latin Emperor, Baldwin of Flanders, wore a cloak embroidered with eagles for his coronation; his daughters used the same device in their arms; and the Byzantine historian Niketas Choniates reports that the Latin emperors struck bronze coins with a double-headed eagle on them.
Tetragrammatic cross
During the Palaiologan period, the insigne of the reigning dynasty, and the closest thing to a Byzantine "national flag", according to Soloviev, was the so-called "tetragrammatic cross", a gold or silver cross with four letters beta "Β" of the same color, one in each corner.As an insigne, the cross was already in frequent use in Byzantium since Late Antiquity. Since the 6th century, crosses with quartered letters are known, especially from coinage, forming the acronyms of various invocations, e.g. quartered "X"s for Σταυρὲ Χριστοῦ χάριν χριστιανούς χάριζε Staurè Christou chárin christianoús chárize or the letters ϹΒΡΔ for Σταυρὲ σου βοήθει Ρωμανόν δεσπότην Staurè sou boíthei Romanón despótin. Images of flags with crosses quartered with golden discs survive from the 10th century, and a depiction of a flag almost identical to the Palaiologan design is known from the early 13th century.
The tetragrammatic cross appears with great frequency in the 14th and 15th centuries: it appears on Byzantine coins during the joint rule of Andronikos II Palaiologos and his son Michael IX Palaiologos, on several west-European portolans to designate Constantinople and other Byzantine cities, above one of the windows of the Palace of the Porphyrogenitus, and is described by pseudo-Kodinos as "the customary imperial banner". On coins, the "B"s were often accompanied by circles or stars up to the end of the Empire, while west-European sources sometimes depict the Byzantine flag as a simple gold cross on red, without the "B"s. The symbol was also adopted by Byzantine vassals, like the Gattilusi who ruled Lesbos after 1355, or the Latin lords of Rhodes Vignolo dei Vignoli and Foulques de Villaret. It was placed on the walls of Galata, apparently as a sign of the Byzantine emperor's—largely theoretical—suzerainty over the Genoese colony. Along with the double-headed eagle, the tetragrammatic cross was also adopted as part of their family coat of arms by the cadet line of the Palaiologos dynasty ruling in Montferrat. It was also adopted in Serbia, with slight changes.
The interpretation of the emblem's symbolism hinges on the identification of the four devices either as letters or as firesteels, a dispute where even contemporary sources are inconsistent, and which has led to much scholarly debate since the time of the 17th-century scholars Du Cange and Marcus Vulson de la Colombière. Thus a late 15th-century French source explicitly refers to them as letters, but a mid-14th century Sevillan traveller and pseudo-Kodinos both call them firesteels. Nevertheless, as Philip Grierson points out, the use of letters by the Greeks as symbols was a long-established practice, and their identifications as firesteels by Kodinos probably reflects west-European influence. The two traditional readings of the four "B"s, Βασιλεὺς βασιλέων βασιλεύων βασιλεύουσιν Basileùs basiléon basileúon basileúousin and Βασιλεὺς βασιλέων βασιλευόντων βασιλεύει Basileùs basiléon basileuónton basileúei were demonstrated by the Greek archaeologist and numismatist Ioannis Svoronos to be later interpretations by Marcus Vulson de la Colombière. Svoronos himself proposed three alternate readings by incorporating the symbol of the cross into the motto: Σταυρὲ βασιλέως βασιλέων βασιλεῖ βοήθει, Σταυρὲ βασιλέως βασιλέων βασιλευούσῃ βοήθει Staurè basileùs basiléon basileuoúse boéthei , and Σταυρὲ βασιλέως βασιλέων βασιλεύων βασίλευε Staurè basileùs basiléon basileúon basíleue, while the Greek heraldist G. Tipaldos rejected Svoronos' reading and suggested that they represented a repetition of the motto Σταυρέ, βοήθει Staurè, boéthei.