The Exaltation of the Cross – so it has been termed in the liturgical revisions after Vatican II – dates back to the time of Constantine, when his mother, Helena, on a pilgrimage to Jerusalem in 326, by apparently miraculous means discovered the wood upon which Christ had been crucified three centuries before. This was one year after the Council of Nicaea, which declared Christ one and for all to be homoousios, ‘consubstantial’ with the Father, God from God, Light from Light, true God from true God, put to death and raised up for our salvation.
This feast also commemorates the

Praise the Lord