Roodmas (from Old English rood "rod", "cross" and mas, Mass; similar to the etymology of Christmas), was the celebration of the Feast of the Cross observed on May 3 in some Christian churches and rites, particularly the historical Gallican Rite of the Catholic Church. It commemorates the finding by Saint Helena of the True Cross in Jerusalem in 355.
The feast originally commemorated the dedication of the Basilica of the Resurrection, and was linked with the finding of the Cross shortly thereafter. Saint Helena reportedly found the Cross on May 3, 355, but most Catholic and Eastern Orthodox rites celebrate the Feast of the Cross on September 14, commemorating the day in 628 when a piece of the Cross taken by the Persian Empire was recovered by the Byzantine Emperor Heraclius.
After the Gallican and Latin Rites were combined, the days were observed individually as the Finding of the Holy Cross (May 3) and the Triumph of the Cross (September 14). Some Protestant churches followed this practice; the Church of England's Book of Common Prayer places Roodmas on May 3.
In 1960, Pope John XXIII combined both Latin Rite celebrations into the September 14 feast, in line with his revisions to the General Roman Calendar that, among other things, eliminated duplicate feasts. The Church of England followed suit with the adoption of the Common Worship liturgy in 2000.