The cross on which Christ died was a major impulse of the crusade movement, a symbol of the Frankish states of Outremer, and an important element of devotion to the Holy Land.
According to Eusebius of Caesarea (d. 339), the Roman emperor Constantine the Great chose the cross as his military insignia and standard following a vision, and Cyril of Jerusalem (d. c. 386) was the first to relate that the True Cross itself had been discovered. This event, which must have occurred before the middle of the fourth century and which two generations later was ascribed to St. Helena (d. 329), stimulated devotion to the True Cross both in Palestine and in the Latin West. When the Persians conquered Jerusalem in 614, the relic was abducted, but Emperor Heraclius (d. 641) recovered it in the course of a counteroffensive in 628. When Jerusalem fell to the Muslim Arabs (c. 637) the relic was sent to Constantinople for safety. These occurrences only intensified the cult of the True Cross: from the seventh century onward, the Exaltation of the Cross (Lat. Exaltatio sanctae Crucis) was celebrated liturgically in both Eastern and Western Christendom; the Discovery of the Cross (Lat. Inventio sanctae Crucis) was also commemorated in some areas, and hymns or poems reinforced popular devotion. Particles of the True Cross formed part of processions and other liturgical acts, particularly in Rome and Constantinople, and relics of the True Cross were also carried into battle even before the First Crusade (1096-1099), both in Byzantium and in Christian Spain. Thus, it is not surprising that participants in the First Crusade carried relics of the True Cross to the East, just as crusaders from Germany and Flanders did when they made their way to the Holy Land in the course of the so-called Second Crusade (1147-1149).
The conquest of Jerusalem by the Christians in 1099 substantially promoted the cult of the True Cross. In the summer of that year, a fragment of the cross came to light, which was entrusted to the Latin patriarch and the chapter of the Church of the Holy Sepulchre. This relic had supposedly been hidden in the seventh century before the Muslims took the town, and the major part was sent to Constantinople; it now became the symbol and liturgical focal point of the kingdom of Jerusalem. In the principality of Antioch, a separate particle was taken into battle as a palladium, only to be lost in battle at the Field of Blood on 28 June 1119. The Jerusalem relic, however, continued to serve liturgical, political, and military functions. It was kept in the Church of the Holy Sepulchre, where it was an object of devotion for pilgrims and was watched over by the canons of the church. The patriarch and his chapter sometimes presented particles of the Cross to prominent visitors or sent staurotheques (reliquaries in the form of a double cross, which held a part of the original wood of the Cross) to the West, especially to priories of their own order.
The main Jerusalem relic, the “wood of the Lord” (Lat. lignum Domini), played a central part in the religious life of the kingdom during celebrations and processions; on occasions it also left the Holy City, most notably during military crises. It first served as battle insignia at the victory of Ascalon of 1099, and subsequently was taken on military expeditions no less than thirty-one times. It also accompanied the army on the ill-fated march to Hattin, where it was seized by the Muslims on 4 July 1187. In spite of diplomatic efforts to recover it, the Jerusalem relic remained lost. However, devotion to the True Cross remained strong, and fragments of it continued to be used, among other things, to emphasize crusade preaching. The flow of reliquaries from Constantinople to the West persisted and reached its climax as a result of the town’s sack and pillage in 1204.