Around the year AD 135, the Romans had built pagan shrines over many of the sites in Israel that were especially significant to the Christians.
Constantine was the first Roman Emperor to take on the Christian faith. During his reign, his mother Helena went to Israel with the purpose of finding the places that are especially significant to Christians, and visited many of these pagan shrines. She located, close together, what she believed to be the sites of the Crucifixion and of the Burial. She then had the Church of the Holy Sepulchre built over these two sites. This church was dedicated on 14 September in the year AD 335.
Since then 14 September has become a day for recognizing the Cross as a symbol of triumph and a sign of Christ's victory over death. 14 September is meant to be a celebration of the Cross, unlike Good Friday, which is a much more solemn day.