A table or stand on which sacrifice is offered. In Catholic churches the table on which the Sacrifice of the Mass is offered. One or more relics of martyrs are commonly set into the altar. In the primitive church and in the catacombs, the altar was usually a niche covered with a slab over the tomb of a martyr. Altar in the Greek Rite is synonymous with sanctuary in the Latin Rite. It may also refer to a secondary side space or section in the transept of the church dedicated to a saint.
With the liturgical changes introduced by the Second Vatican Council, the Holy See has issued detailed directives on the construction and adornment of the altar:
"In a consecrated building the altar on which the Eucharist is celebrated may be fixed or movable; in any other place, especially if Mass is not normally celebrated there, a convenient table may be used, but it must be covered with a cloth and a corporal.
"An altar is said to be fixed if it is in fact fixed to the floor so that it cannot be moved; it is said to be movable if it can in fact be moved.
"The main altar should be freestanding, away from any wall, so that the priest can walk all around it and can celebrate facing the people. It should be in a position such that the entire congregation will naturally focus their attention on it. Normally the main altar should be both fixed and consecrated.
"The table of a fixed altar should be made of natural stone; this accords with age-long practice of the Church and its own symbolic meaning. Nevertheless the Bishops' Conference may authorize the use of some other generally accepted and solid material susceptible of good workmanship. The structure supporting the table may be of any material so long as it is solid and durable.
"A movable altar may be made from any material which is solid and dignified, suitable for liturgical use and acceptable to local traditions and culture.
"Both fixed and movable altars should be consecrated by the rites provided in the Roman Pontifical, but it suffices merely to bless an altar if it is movable. There is no obligation to incorporate a consecrated stone in a movable altar or to place such a stone on a table used for celebrating Mass in a non-consecrated building.
"The custom of putting relics of saints, whether martyrs or not, into or underneath consecrated altars is to be commended. But it is important to verify the authenticity of the relics.
"Minor altars should be few in number; in new churches they should be located in chapels somewhat apart from the nave of the church.
"Out of reverence for the Mass which is both sacrifice and sacred meal the altar must be covered with at least one cloth. Its shape, size and ornamentation should be in keeping with the structure of the altar.
"In all liturgical celebrations candles are required to express reverence and to indicate the various degrees of solemnity. These may be put on the altar or placed near it as may best suit the structure of the altar and the character of the sanctuary. The candles must not impede the people's view of the altar or anything placed on it.
"A cross, easily visible to the people, should be on the altar or somewhere not far from it" (Institutio Generalis Missalis Romani, 1969, Nos. 260-70). (Etym. Anglo-Saxon altare, altar; Latin altar or altare, an altar, high place.)