Versus populum

Versus populum (Latin for "towards the people") is the liturgical orientation in which the priest celebrates Mass facing the people. The opposite orientation, whereby the priest faces in the same direction as the people, is often called ad orientem ("towards the east"), even if the priest is not in fact facing the east.

From the middle of the 17th century, almost all new Latin-rite altars were built against a wall or backed by a reredos, with a tabernacle placed on the altar or inserted into the reredos. This meant that the priest turned to the people, putting his back to the altar, only for a few short moments at Mass. However, the Tridentine Missal itself speaks of celebrating versus populum, and gives corresponding instructions for the priest when performing actions that in the other orientation involved turning around in order to face the people.

It has been said that the reason the Pope always faced the people when celebrating Mass in St Peter's was that early Christians faced eastward when praying and, due to the difficult terrain, the basilica was built with its apse to the west. Some have attributed this orientation in other early Roman churches to the influence of Saint Peter's. However, the arrangement whereby the apse with the altar is at the west end of the church and the entrance on the east is found also in Roman churches contemporary with Saint Peter's (such as the original Basilica of Saint Paul Outside the Walls) that were under no such constraints of terrain, and the same arrangement remained the usual one until the sixth century. In this early layout, the people were situated in the side aisles of the church, not in the central nave. While the priest faced both the altar and east throughout the Mass, the people would face the altar (from the sides) until the high point of the Mass, where they would then turn to face east along with the priest.

It was only in the 8th or 9th century that the position whereby the priest faced the apse, not the people, when celebrating Mass was adopted in the Roman Rite. The new usage was introduced from the Frankish Empire and later became almost universal in the West. However, in several churches in Rome, it was physically impossible, even before the twentieth-century liturgical reforms, for the priest to celebrate Mass facing away from the people, because of the presence, immediately in front of the altar, of the "confession" (Latin: confessio), an area sunk below floor level to enable people to come close to the tomb of the saint buried beneath the altar. The best-known such "confession" is that in St Peter's Basilica, but many other churches in Rome have the same architectural feature, including at least one, the present Basilica of Saint Paul Outside the Walls, which, although the original Constantinian basilica was arranged like St Peter's, is oriented since 386 in such a way that the priest faces west when celebrating Mass.

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