The Latin cross (crux immissa), upright with a lower limb longer than the other three, is the predominant Christian sign, but its dominance is not original. The earliest Christians were reluctant to depict the cross at all: crucifixion was a servile and shameful Roman penalty, and for the first two to three centuries believers more often used the fish, the anchor and the Chi-Rho monogram. The tau-rho staurogram appears as an abbreviation in New Testament papyri around the year 200. Public display of the cross followed Constantine's legalisation of Christianity and his abolition of crucifixion as a punishment in the fourth century. The crucifix, the cross bearing the body of Christ, is later still, becoming common only from roughly the sixth to tenth centuries; earlier crosses were bare or jewelled (crux gemmata), emphasising triumph rather than suffering.
The Alexamenos graffito, a piece of mocking graffiti scratched into Palatine Hill plaster and generally dated to the second or third century, shows a Christian worshipping a crucified, donkey-headed figure, evidence that outsiders already linked Christians to a crucified god well before the cross became a public devotional image. The staurogram, overlaying the Greek letters tau and rho so the tau's crossbar reads as outstretched arms, functioned as a pictogram of the crucifixion embedded in New Testament manuscript text centuries before free-standing crosses appeared, a transitional stage between avoiding the image and displaying it. Eusebius records Constantine's vision of a cross-shaped sign before the Battle of the Milvian Bridge in 312, an episode later ages treated as the hinge toward the cross's emergence as a public emblem, though Eusebius wrote decades after the event and its details were already disputed in antiquity.