Its significance lies in the belief that Jesus Christ was executed by the Romans on a large wooden cross. According to the Bible, the manner of Christ's death was "crucifixion", which involved being tied or (in Christ's case) nailed to the cross, and left to die. This painful method of execution was common in the Roman Empire at the time.
In Eastern Orthodox Christianity, the cross represents Christ's victory over death and sin, since it is believed that through His death he conquered death itself. Catholic and Orthodox Christians often make the sign of the cross by moving their right hand so as to draw a cross upon themselves. One of the twelve great feasts in the Eastern Orthodox Church is the Exaltation of the Cross on September 14, which commemorates the discovery of the (supposedly) original cross in 326.