Christogram

A Christogram 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. These symbols are ancient and go back thousands of years to the Celtic 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 CE. 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, spelt 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.

Chi Rho Symbol
The Chi Rho (☧) is one of the earliest forms of Christogram, formed by superimposing the first two (capital) letters—chi and rho (ΧΡ)—of the Greek word ΧΡΙΣΤΟΣ (Christos) in such a way that the vertical stroke of the rho intersects the center of the chi.

In pre-Christian times, the Chi-Rho symbol was also used to mark a particularly valuable or relevant passage in the margin of a page, abbreviating chrēston (good). Some coins of Ptolemy III Euergetes (r. 246–222 BC) were marked with a Chi-Rho.

Although formed of Greek characters, the device (or its separate parts) is frequently found serving as an abbreviation in Latin text, with endings added appropriate to a Latin noun, thus XPo, signifying Christo, "to Christ", the dative form of Christus, or χρ̅icola, signifying Christicola.

Insular Gospel books
In Insular Gospel books, the beginning of Matthew 1:18, at the end of his account of the genealogy of Christ and introducing his account of the life, so representing the moment of the Incarnation of Christ, was usually marked with a heavily decorated page, where the letters of the first word "Christi" are abbreviated and written in Greek as "XPI", and often almost submerged by decoration. Though the letters are written one after the other and the "X" and "P" not combined in a monogram, these are known as Chi-Rho pages.

Famous examples are in the Book of Kells and Book of Lindisfarne. The "X" was regarded as the crux decussata, a symbol of the cross; this idea is found in the works of Isidore of Seville and other patristic and Early Medieval writers. The Book of Kells has a second Chi-Rho abbreviation on folio 124 in the account of the Crucifixion of Christ, and in some manuscripts the Chi-Rho occurs at the beginning of Matthew rather than mid-text at Matthew 1:18. In some other works like the Carolingian Godescalc Evangelistary, "XPS" in sequential letters, representing "Christus" is given a prominent place.