 The area around the altar is seen as endowed with greater holiness, and is usually physically distinguished from the rest of the church, whether by a permanent structure such as an iconostasis, a rood screen, altar rails, a curtain that can be closed at more solemn moments of the liturgy (as in the Armenian Apostolic Church and Armenian Catholic Church), or simply by the general architectural layout.The altar is often on a higher elevation than the rest of the church.Churches generally have a single altar, although in the Western branches of Christianity, as a result of the former abandonment of concelebration of Mass, so that priests always celebrated Mass individually, larger churches have had one or more side chapels, each with its own altar.