The labarum (Greek: λάβαρον) was a vexillum (military standard) that displayed the "Chi-Rho" symbol ☧, a christogram formed from the first two Greek letters of the word "Christ" (Greek: ΧΡΙΣΤΟΣ, or Χριστός) — Chi (χ) and Rho (ρ).[2] It was first used by the Roman emperor Constantine the Great. Source : https://en.wikipedia.org/wiki/Labarum
