In the Catholic liturgy

Catholic liturgy

The Catholic Church is fundamentally liturgical and sacramental in its public life of worship.-Liturgical principles:As explained in greater detail in the Catechism of the Catholic Church and its shorter Compendium, the liturgy is something that "the whole Christ", Head and Body, celebrates —...

 the expression ad orientem (Latin

Latin

Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...

 for "to the east") is the eastward orientation of a priest celebrating Mass

Mass (liturgy)

"Mass" is one of the names by which the sacrament of the Eucharist is called in the Roman Catholic Church: others are "Eucharist", the "Lord's Supper", the "Breaking of Bread", the "Eucharistic assembly ", the "memorial of the Lord's Passion and Resurrection", the "Holy Sacrifice", the "Holy and...

. This orientation has been described as the "cosmic sign of the rising sun which symbolizes the universality of God."

The expression ad orientem is often used instead to mean facing the apse or wall behind the altar, with priest and people looking in the same direction, even if not to the east, even when they have their backs to the east. Thus, when Pope Benedict XVI

Pope Benedict XVI

Benedict XVI is the 265th and current Pope, by virtue of his office of Bishop of Rome, the Sovereign of the Vatican City State and the leader of the Catholic Church as well as the other 22 sui iuris Eastern Catholic Churches in full communion with the Holy See...

 celebrated Mass in the Sistine Chapel

Sistine Chapel

Sistine Chapel is the best-known chapel in the Apostolic Palace, the official residence of the Pope in Vatican City. It is famous for its architecture and its decoration that was frescoed throughout by Renaissance artists including Michelangelo, Sandro Botticelli, Pietro Perugino, Pinturicchio...

 on 13 January 2008, his choice of orientation was described as ad orientem, although he was in fact facing the west wall of the chapel.

The ad orientem orientation is opposed to that called versus populum

Versus populum

Versus populum 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 , even if the priest is not in fact facing the east.From the middle of the...

, in which the celebrating priest faces the people.

History

The earliest churches in Rome had a façade to the east and an apse with the altar to the west; the priest celebrating Mass stood behind the altar, facing east and so towards the people.

In 7th century England

England

England is a country that is part of the United Kingdom. It shares land borders with Scotland to the north and Wales to the west; the Irish Sea is to the north west, the Celtic Sea to the south west, with the North Sea to the east and the English Channel to the south separating it from continental...

, Catholic churches were built so that on the very feast day of the saint in whose honor they were named, Mass could be offered on an altar while directly facing the rising sun.

It was 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 Basilicas. This usage was introduced from the Frankish Empire

Frankish Empire

Francia or Frankia, later also called the Frankish Empire , Frankish Kingdom , Frankish Realm or occasionally Frankland, was the territory inhabited and ruled by the Franks from the 3rd to the 10th century...

 and later became almost universal in the West. However, the Tridentine

Tridentine Mass

The Tridentine Mass is the form of the Roman Rite Mass contained in the typical editions of the Roman Missal that were published from 1570 to 1962. It was the most widely celebrated Mass liturgy in the world until the introduction of the Mass of Paul VI in December 1969...

 Roman Missal

Roman Missal

The Roman Missal is the liturgical book that contains the texts and rubrics for the celebration of the Mass in the Roman Rite of the Catholic Church.-Situation before the Council of Trent:...

 continued to recognize the possibility of celebrating Mass "versus populum

Versus populum

Versus populum 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 , even if the priest is not in fact facing the east.From the middle of the...

" (facing the people), and 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" , an area sunk below floor level to enable people to come close to the tomb of the saint buried beneath the altar.
The present-day Roman Missal does not forbid the ad orientem position for the priest when saying Mass and only requires that in new or renovated churches the facing-the-people orientation be made possible: "The altar should be built apart from the wall, in such a way that it is possible to walk around it easily and that Mass can be celebrated at it facing the people, which is desirable wherever possible." As in some ancient churches the ad orientem position was physically impossible, so today there are churches and chapels in which it is physically impossible for the priest to face the people throughout the Mass.

A letter of 25 September 2000 from the Congregation for Divine Worship and the Discipline of the Sacraments treats the phrase "which is desirable wherever possible" as referring to the requirement that altars be built apart from the wall, not to the celebration of Mass facing the people, while "it reaffirms that the position toward the assembly seems more convenient inasmuch as it makes communication easier ... without excluding, however, the other possibility."

On 13 January 2008, Pope Benedict XVI publicly celebrated Mass in the Sistine Chapel

Sistine Chapel

Sistine Chapel is the best-known chapel in the Apostolic Palace, the official residence of the Pope in Vatican City. It is famous for its architecture and its decoration that was frescoed throughout by Renaissance artists including Michelangelo, Sandro Botticelli, Pietro Perugino, Pinturicchio...

 at its altar, which is attached to the west wall. He has since celebrated Mass at the same altar in the Sistine Chapel annually for the Feast of the Baptism of the Lord

Baptism of the Lord

The Baptism of the Lord is the feast day commemorating the baptism of Jesus in the Jordan River by John the Baptist. Originally the baptism of Christ was celebrated on Epiphany, which commemorates the coming of the Magi, the baptism of Christ, and the wedding at Cana...

. On 1 December 2009, he celebrated Mass in the Pauline Chapel in the Apostolic Palace. It was the first time that this Pope publicly celebrated Mass ad orientem on a freestanding altar. He celebrated Mass facing the altar again in the Pauline Chapel on 15 April 2010.