Labarum

This article is about the vexillum. For the ΧΡ symbol, ☧, see Chi Rho.

The Labarum of Constantine I, reconstructed from the depiction on a follis minted c. 337. The three dots represent "medallions" which are said to have shown portraits of Constantine and his sons.

The labarum (Byzantine Greek: λάβαρον or λάβουρον) was a vexillum (military standard) that displayed the "Chi-Rho" symbol ☧, a christogram formed from the first two Greek letters of the word "Christ" (Byzantine Greek: ΧΡΙΣΤΟΣ, or Χριστός) – Chi (χ) and Rho (ρ). It was first used by the Roman emperor Constantine the Great.

Ancient sources draw an unambiguous distinction between the two terms labarum and Chi-Rho, even though later usage sometimes regards the two as synonyms. The name labarum was applied both to the original standard used by Constantine the Great and to the many standards produced in imitation of it in the Late Antique world, and subsequently.