 "devotees of the Cross".In his book "De Corona", written in 204, Tertullian tells how it was already a tradition for Christians to trace repeatedly on their foreheads the sign of the cross.So closely associated with Christ was the cross that Clement of Alexandria, who died between 211 and 216, could without fear of ambiguity use the phrase "τὸ κυριακὸν σημεῖον" (the Lord's sign) to mean the cross, when he repeated the idea, current as early as the Epistle of Barnabas, that the number 318 (in Greek numerals, ΤΙΗ) in was a foreshadowing (a "type") of the cross (T, an upright with crossbar, standing for 300) and of Jesus (ΙΗ, the first two letter of his name ΙΗΣΟΥΣ, standing for 18).