In the early 3rd century, Clement of Alexandria, used the phrase "" (the Lord's sign) to mean the cross. He used the phrase when discussing that the number 318 (in Greek numerals, ΤΙΗ) in was a foreshadowing of the cross and Jesus. T is the Greek number fore 300. ΙΗ, the first two letters of Jesus's name ΙΗΣΟΥΣ, means 18. Tertullian called the Christian believers "crucis religiosi", "i.e." "devotees of the Cross". In his book "De Corona", Tertullian tells how it was a tradition for Christians to trace the sign of the cross on their foreheads.