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. One of the oldest Christograms is the Chi-Rho (☧). It consists of the superimposed Greek letters chi and rho , which are the first two letters of the Greek , 'Christ'. It was displayed on the military standard used by Constantine I in 312 CE. The IX monogram () is a similar form, using the initials of the name , 'Jesus (the) Christ', as is the ΙΗ monogram (), using the first two letters of the name , '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 in Greek capitals, has the abbreviations IHS (also written JHS, IHC, or ΙΗΣ), the name Christus , spelt , 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 in both Greek and Cyrillic tradition. A Middle Latin term for abbreviations of the name of Christ is . Similarly, the Middle Latin , refers to the Chi-Rho monogram specifically. Chi (Χ) In antiquity, the cross, i.e. the instrument of Christ's crucifixion (, ), 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". In Plato's , it is explained that the two bands which form the "world soul" () cross each other like the letter Chi, possibly referring to the ecliptic crossing the celestial equator: Justin Martyr in the 2nd century makes explicit reference to Plato's image in in terms of a prefiguration of the Holy Cross. An early statement may be the phrase in Didache, "sign of extension in heaven" (). An alternative explanation of the intersecting celestial symbol has been advanced by George Latura, claiming that Plato's "visible god" in is the intersection of the Milky Way and the Zodiacal Light, a rare apparition important to pagan beliefs. He said that