The Byzantine imperial ensign (βασιλικόν φλάμουλον), as depicted in the 14th-century Castilian Book of All Kingdoms, and described in the Treatise on Offices by the mid 14th-century Byzantine writer Pseudo-Kodinos as being hoisted on imperial naval vessels. It features the tetragrammic cross with the four "B"s that is attested in contemporary portolans, on coins and reliefs.
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Cplakidas