In military organizations, the practice of carrying colours, standards, flags, or guidons, both to act as a rallying point for troops and to mark the location of the commander, is thought to have originated in Ancient Egypt some 5,000 years ago. The Roman Empire also made battle standards reading SPQR a part of their vast armies. It was formalized in the armies of Europe in the High Middle Ages, with standards being emblazoned with the commander's coat of arms.
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The draco ("dragon" or "serpent", plural dracones) was a military standard of the Roman cavalry. Carried by the draconarius, the draco was the standard of the cohort, as the eagle (aquila) was that of the legion.
The draco may have been introduced to the Roman army after the Dacian Wars by Dacian (see Dacian draco) and Sarmatian units in the second century. According to Vegetius, in the fourth century a draco was carried by each legionary cohort.
The Chi Rho (☧, English pronunciation /ˈkaɪ ˈroʊ/ KY-roh; also known as chrismon) is one of the earliest forms of the Christogram, formed by superimposing the first two (capital) letters—chi and rho (ΧΡ)—of the Greek ΧΡΙΣΤΟΣ (rom: Christos) in such a way that the vertical stroke of the rho intersects the center of the chi.
The Chi Rho symbol was used by the Roman Emperor Constantine the Great (r. 306–337 AD) as part of a military standard (vexillum). Constantine's standard was known as the Labarum. Early symbols similar to the Chi Rho were the Staurogram (
) and the IX monogram (
).