The original form of the Cross was that of the letter T. The numerical value of the sign T (Tau), in Greek arithmetic was 300. Eighteen was represented by ιη, the first two letters of the name ᾽Ιησοὐς, Jesus. To St. Ambrose, therefore, it seemed that there was some mysterious power in the number 318, represented by the sign of the Cross and the first two letters of the Saviour’s name, thus—TIH.