I. Liturgy

The invocation “Lord have mercy” is frequent and widespread in the Christian liturgies. It often belongs to the litany (as described by the pilgrim Egeria in the context of 4th-century candelabra ceremonies in Jerusalem) and is known in this form both in the East and in the West (e.g. Benedict, Rule of Saint, chs. 9, 12, 18). It may have been in use as a response in the litany as early as the 5th century; some acclamations were sung by the congregation. By the 8th century ( Ordo Romanus Primus ) it had becom…