Chi-Rho

The Chi-Rho superimposes the first two Greek letters of Christos, X, chi, and P, rho, into a single monogram, one of the oldest Christograms, in Christian use by the early fourth century and possibly before. Its rise is bound to the emperor Constantine: the Christian writers Lactantius and Eusebius report that before the battle of the Milvian Bridge in 312 he was directed by a vision or dream to mark his soldiers with a heavenly sign, and the labarum, the imperial military standard, thereafter carried the Chi-Rho. The accounts differ in detail and cannot be fully reconciled, which is itself worth noting: the tradition that fixed the emblem to Constantine's victory was written down by partisan authors after the fact.

The letters chi and rho had circulated earlier still as an ordinary scribal abbreviation in Ptolemaic and Roman Egyptian documentary papyri, marking words beginning with those letters, but no verified specifically Christian Chi-Rho monument is older than Constantine's reign, so claims of pre-Constantinian Christian use rest on inference rather than surviving artifacts. A related but distinct sign, the staurogram, overlaying tau and rho so the crossbar reads as outstretched arms, is demonstrably older: it appears embedded in the text of New Testament papyri such as Bodmer P66, copied around the year 200, making it Christianity's earliest surviving visual reference to the crucifixion, a full century before the Chi-Rho's public debut.

Once imperial favour made it safe, the Chi-Rho spread rapidly across the fourth-century Christian world, on coins, sarcophagi, lamps, mosaics and the apses of churches, often flanked by the Greek letters alpha and omega, the first and the last of the Book of Revelation, and sometimes enclosed in a victory wreath. It frequently stands beside the tau-rho staurogram and the iota-chi monogram. As Christianity became the religion of empire the monogram carried a triumphal rather than a suffering sense, akin to the jewelled cross of the same period.

In later Western use it survives especially in manuscript ornament: the Chi-Rho page of the Book of Kells, filling an entire folio with interlace grown out of the monogram's two letters, is among the most celebrated single pages in all of Insular art, and the same device recurs at smaller scale across Carolingian and Ottonian gospel books as the conventional way to mark the opening of Matthew's genealogy of Christ, the point in the text where the name Christos first occurs. The monogram remains in active liturgical use: it appears stamped on paschal candles blessed at the Easter Vigil in the Catholic and many Anglican rites, flanked there by alpha, omega and the numerals of the current year, a modern continuation of the same abbreviating impulse that first put chi and rho together in a scribe's hand centuries before Constantine gave it an empire.