[[Image:Labarum.jpg|right|thumb|''Chi-Rho,'' the first two letters of [[Jesus Christ]] in Greek, which [[Constantine the Great|Constantine]] saw in a vision along with the words ''"in this sign you will conquer".'']]

The Labarum of [[Constantine the Great]] was a [[w:Vexillum|vexillum]]<ref group="note">The [[w:Vexillum|vexillum]] (plural vexilla) was a military standard (flag, banner) used in the Classical Era of the Roman Empire. On the vexillum the cloth was draped from a horizontal crossbar suspended from the staff; this is unlike most modern flags in which the 'hoist' of the cloth is attached directly to the vertical staff. The bearer of a vexillum was known as a ''vexillarius''. The vexillum was a treasured symbol of the military unit that it represented and it was closely defended in combat.</ref> that displayed the "[[w:Chi Rho|Chi-Rho]]" [[w:Christogram|Christogram]], formed from the first two Greek letters of the word "[[Jesus Christ|Christ]]" (Greek: '''ΧΡ'''ΙΣΤΟΣ, or '''Χρ'''ιστός) — [[w:Chi (letter)|Chi]] (χ) and [[w:Rho (letter)|Rho]] (ρ). Fashioned after legionary standards, it substituted the from of a [[cross]] for the old pagan symbols, surmounted by a jewelled wreath containing the monogram of Christ, intersecting '''Chi''' (χ) and '''Rho''' (ρ), on which hung a purple banner beset with gold trim and embroidery, inscribed with ''' ''"Εν Τουτω Νικα"'' (''in hoc signo vinces'') — "In this sign, conquer." '''