The Cross of Tau, named after the Greek letter it resembles, is suspected to have originated with the Egyptians. It has been a symbol to many cultures before Christianity, including a mention in the Old Testament book of Ezekiel. It has been adopted by Christianity as a representation of the Cross. It is strongly identified with the bull in the astrological sign of Taurus.
It is said by St. Jerome and other Catholic Church Fathers that the Tau is an Old Testament allusion to the cross and crucifixion of Jesus mentioned in Ezekiel. "Mark Thau upon the foreheads of the men that sigh". (Ezekiel 9:4 DRA)
The use of the Tau Cross in Christianity dates back to the latter's beginnings. St. Anthony of Egypt bore a cross in the form of a tau on his cloak. The Tau Cross is most commonly used in reference to the Franciscan Order and Saint Francis of Assisi, who adopted it as his personal coat of arms after hearing Pope Innocent III talk about the Tau symbol. It is now used as a symbol of the Franciscan Order.
The tau cross is often used as a variant of the Latin, or Christian cross.
The Cross of Tau is also called the Tau Cross, St. Anthony's Cross, the Old Testament Cross, the Anticipatory Cross, the Cross Commissee, the Egyptian Cross, the Advent Cross, Croce taumata, "Saint Francis's Cross" or the Crux Commissa. Hence, this cross is often used during the Advent season. It also appears on the arms of the ancient de Lemos clan of Spain and Portugal, which according to family sites also represents a meeting place and the balance of justice and trade.
As with Christianity, other ancient societies who used the "Tau" symbol also expanded upon its symbolism to include life, resurrection, reincarnation, and blood sacrifice. These crosses are rare, and only a few are left in the world, the most well known being the cross on Tory Island in County Donegal, Ireland.