The Christian cross,

Seen as a representation of the crucifixion of Jesus on a large wooden  cross, is a renowned symbol of Christianity. It is related to the crucifix (a  cross that includes a corpus, usually a three-dimensional representation of  Jesus body) and to the more general family of cross symbols, the term cross  itself being detached from the original specifically Christian meaning in modern  English. The basic forms of the cross are the Latin cross with unequal arms and  the Greek cross with equal arms, besides numerous variants, partly with  confessional significance, such as the tau cross, the double-barred cross,  triple-barred cross, cross-and-crosslets, and many heraldic variants, such as  the cross potent, cross pattee, cross moline, cross fleury, etc. For a few  centuries, the emblem of Christ was a headless T-shaped Tau cross rather than a  Latin cross. Elworthy considered this to originate from Pagan Druids who made  Tau crosses of oak trees stripped of their branches, with two large limbs  fastened at the top to represent a mans arm; this was Thau, or God.

Source  Wikipedia