The Great (or Royal) Hours are a particularly solemn celebration in the Eastern Orthodox Church. The Great Hours are celebrated only three times a year: on the Eve of the Nativity, the Eve of Theophany, and Great Friday.
At each of the Hours, one of the three fixed Psalms is replaced by a Psalm that is significant to the Feast being celebrated (in this case, Great Week); the Troparion and Kontakion of the day are replaced by numerous hymns chanted by the choir; and each Hour has an Old Testament reading, a Prokeimenon, and an Epistle and Gospel.
