The cross is one of the most ancient human symbols, and is used by many religions, most notably Christianity. The cross represents Christ's victory over death and sin, since it is believed that through His death he conquered death itself.
During the first three centuries of Christianity, the cross was rare in Christian iconography, although descriptions of it are found in Christian writings from the early 2nd century onwards.
The Cross first became prominent in Christian imagery during the 3rd century. An early third century reference is in Clement of Alexandria's unfinished 'Miscellanies' (book VI), where he speaks of the Cross as "the symbol of the Lord." His contemporary Tertullian could designate the body of Christian believers as "devotees of the Cross" .
Christian books from Armenia and Syria contained evidence that the cross originated with horsemen from the east, possibly referring to the first Turkic people. In old Armenian temples, some stylistic Turkic influences are found in cross symbols.
A crucifix or cross is considered by some Christians as one of the most effective ways of warding off evil.
Information source: Wikipedia