Chrismon
Chi-Rho symbol with Alpha and Omega on a 4th-century sarcophagus (Vatican Museums)

A Christogram (Latin: Monogramma Christi)[a] is a monogram or combination of letters that forms an abbreviation for the name of Jesus Christ, traditionally used as a religious symbol within the Christian Church.

One of the oldest Christograms is the Chi-Rho (☧). It consists of the superimposed Greek letters chi (Χ) and rho (Ρ), which are the first two letters of the Greek χριστός, 'Christ'. It was displayed on the labarum military standard used by Constantine I in 312 AD. The IX monogram () is a similar form, using the initials of the name Ἰησοῦς (ὁ) Χριστός, 'Jesus (the) Christ', as is the ΙΗ monogram (), using the first two letters of the name ΙΗΣΟΥΣ, 'JESUS' in uppercase.

There were a very considerable number of variants of "Christograms" or monograms of Christ in use during the medieval period, with the boundary between specific monograms and mere scribal abbreviations somewhat fluid.

The name Jesus, spelled ΙΗΣΟΥΣ in Greek capitals, has the abbreviations IHS (also written JHS, IHC, or ΙΗΣ). The name Christus, spelt ΧΡΙΣΤΟΣ, has XP (and inflectional variants such as IX, XPO, XPS, XPI, XPM). In Eastern Christian tradition, the monogram ΙϹΧϹ (with Overline indicating scribal abbreviation) is used for Ἰησοῦς Χριστός in both Greek and Cyrillic tradition.

A Middle Latin term for abbreviations of the name of Christ is chrisimus.[1] Similarly, the Middle Latin crismon, chrismon refers to the Chi-Rho monogram specifically.[2]

Symbols

Chi (Χ)

In antiquity, the cross, i.e. the instrument of Christ's crucifixion (crux, stauros), was taken to be T-shaped, while the X-shape ("chiasmus") had different connotations. There has been scholarly speculation on the development of the Christian cross, the letter Chi used to abbreviate the name of Christ, and the various pre-Christian symbolism associated with the chiasmus interpreted in terms of "the mystery of the pre-existent Christ".[3]

In Plato's Timaeus, it is explained that the two bands which form the "world soul" (anima mundi) cross each other like the letter Chi, possibly referring to the ecliptic crossing the celestial equator:

The two great circles of the heavens, the equator and the ecliptic, which, by intersecting each other form a sort of recumbent chi and about which the whole dome of the starry heavens swings in a wondrous rhythm, became for the Christian eye a heavenly cross.

— Rahner 1971, pp. 49–50. See also Grigg 1977, p. 477

Justin Martyr in the 2nd century makes explicit reference to Plato's image in Timaeus in terms of a prefiguration of the Holy Cross.[5] An early statement may be the phrase in Didache, "sign of extension in heaven" (sēmeion epektaseōs en ouranōi).[3]

An alternative explanation of the intersecting celestial symbol has been advanced by George Latura, claiming that Plato's "visible god" in Timaeus is the intersection of the Milky Way and the Zodiacal Light, a rare apparition important to pagan beliefs. He said that Christian bishops reframed this as a Christian symbol.[6]

The most commonly encountered Christogram in English-speaking countries in modern times is the Χ (or more accurately, Chi), representing the first letter of the word Christ, in such abbreviations as Xmas (for "Christmas") and Xian or Xtian (for "Christian").