Saints Constantine and Helen + May 21
O Lord, thy disciple Emperor Constantine, who saw in the sky the Sign of Thy Cross, Accepted the call that came straight from Thee, as it happened to Paul, and not from any man. He built his capital and entrusted it to Thy care. Preserve our country in everlasting peace, through the intercession of the Mother of God, for Thou art the Lover of mankind.
+ Troparion of Ss. Constantine and Helen, Tone 8
"Constantine's legacy can be seen in Christianity's transformation from a private sect into a public church that encompassed the whole of society. He put it on an institutional footing, which enabled the Church to be the leading cultural force in the ancient world."
(From Robert Arakaki's Constantine The Great: Roman Emperor, Christian Saint, History's Turning Point)