Ancient Greek kylix showing a hoplite offering a sacrifice before an altar, around 480 BC. Ancient Agora Museum of Athens in the Stoa of Attalus

The ancient Altar of Pergamon, reconstructed at the Pergamon museum, Berlin.

The Opferstein or Sacrifice Rock at Maria Taferl, Austria. It was used by the ancient Celts to make sacrifices upon and is now located in the plaza of the basilica there.

An altar is any structure upon which offerings such as sacrifices are made for religious purposes. Altars are usually found at shrines, and they can be located in temples, churches and other places of worship. Today they are used particularly in Christianity, Buddhism, Hinduism, Shinto, Taoism, as well as in Neopaganism and Ceremonial Magic. Judaism did so until the destruction of the Second Temple. Many historical faiths also made use of them, including Greek and Norse religion.

In the Hebrew Bible[link]

Horned altar at Tel Be'er Sheva, Israel.

Altars (Hebrew: מזבח‎, mizbe'ah, "a place of slaughter or sacrifice")^[1] in the Hebrew Bible were typically made of earth ^[2] or unwrought stone.^[3] Altars were generally erected in conspicuous places.^[4][5][6][7] The first altar recorded in the Hebrew Bible is that erected by Noah .^[8] Altars were erected by Abraham,^[9] by Isaac,^[10] by Jacob,^[11] and by Moses,^[12] (Adonai-nissi).

After the theophany on Mount Sinai, in the Tabernacle—and afterwards in the Temple—only two altars were used: the Altar of Burnt Offering, and the Altar of Incense.

Christianity[link]

Dedication of an altar

The word "altar", in Greek θυσιαστήριον (see:θυσία), appears twenty-four times in the New Testament. Significantly, Hebrews 13:10 ^[13] shows Christians having an altar of which those who did not believe in Jesus could not partake, a reference to the eternal, once-for-all sacrifice of Jesus Christ, thus fulfilling the sacrificial laws of the Old Testament. In Catholic and Orthodox Christian theology, the Eucharist is a re-presentation, in the literal sense of the one sacrifice being made "present again". Hence, the table upon which the Eucharistic meal (the Bread and the Wine) is eaten is called an altar.

Altars occupy a prominent place in the sanctuaries of many churches, especially those belonging to the ancient Christian traditions, such as the Eastern Orthodox, Oriental Orthodox, Assyrian, Roman Catholic, and Anglican Churches. They are also found in many Protestant worship places. It plays a central role in the celebration of the Eucharist. A priest (or minister in Protestant circles) celebrates at the altar, on which the bread and the wine are placed.

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 or altar rails, by 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. In Reformed and Anabaptist churches, a table, often called a "communion table", serves an analogous function. In some colloquial usage, the word "altar" is used to denote the altar rail also, although this usage is technically incorrect.

Churches generally have a single altar, although in the West, where concelebration had formerly fallen into disuse and priests always celebrated Mass individually, larger churches have had one or more side chapels, each with its own altar. The main altar was also referred to as the "high altar". Since the revival of concelebration in the West, the Roman Missal recommends that in new churches there should be only one altar, "which in the gathering of the faithful will signify the one Christ and the one Eucharist of the Church."^[14] But most existing Western churches, whether Roman Catholic or Anglican, may have a high altar in the main body of the church, with one or more adjoining chapels, each with its own altar, at which the Eucharist may be celebrated on weekdays.

Architecturally, there are two types of altars: those that are attached to the eastern wall of the chancel, and those that are free-standing and can be walked around, for instance when incensing the altar.

Early Coptic altar carved into the wall of the Temple of Isis on the island Philae in Egypt.

In the earliest days of the Church, the Eucharist appears to have been celebrated on portable altars set up for the purpose. Some historians hold that, during the persecutions, the Eucharist was celebrated among the tombs in the Catacombs of Rome, using the sarcophagi (see sarcophagus) of martyrs as altars on which to celebrate. Other historians dispute this, but it is thought to be the origin of the tradition of placing relics beneath the altar.

When Christianity was legalized under Constantine the Great and Licinius, formal church buildings were built in great numbers, normally with free-standing altars in the middle of the sanctuary, which in all the earliest churches built in Rome was at the west end of the church. "When Christians in fourth-century Rome could first freely begin to build churches, they customarily located the sanctuary towards the west end of the building in imitation of the sanctuary of the Jerusalem Temple. Although in the days of the Jerusalem Temple the High Priest indeed faced east when sacrificing on Yom Kippur, the sanctuary within which he stood was located at the western end of the Temple. The Christian replication of the layout and the orientation of the Jerusalem Temple helped to dramatize the eschatological meaning attached to the sacrificial death of Jesus the High Priest in the Epistle to the Hebrews."^[15] The ministers (bishop, priests, deacons, subdeacons, acolytes), celebrated the Eucharist facing east, towards the entrance. Some hold that for the central part of the celebration the congregation faced the same way. After the sixth century the contrary orientation prevailed, with the entrance to the west and the altar at the east end. Then the ministers and congregation all faced east during the whole celebration; and in Western Europe altars began, in the Middle Ages, to be permanently placed against the east wall of the chancel.

In Western Christian churches[link]

Altar of Santa Cecilia in Trastevere

Most rubrics, even in books of the seventeenth century and later, such as the Pontificale Romanum, continued to envisage the altar as free-standing. The rite of the Dedication of the Church ^[16] continued to presume that the officiating Bishop could circle the altar during the consecration of the church and its altar. Despite this, with the increase in the size and importance of the reredos, most altars were built against the wall or barely separated from it.

In almost all cases, the eastward orientation for prayer was maintained, whether the altar was at the west end of the church, as in all the earliest churches in Rome, in which case, the priest celebrating Mass faced the congregation and the church entrance, or whether it was at the east end of the church, in which case the priest faced the eastern apse and had his back to the congregation. This diversity was recognized in the rubrics of the Roman Missal from the 1604 typical edition of Pope Clement VIII to the 1962 edition of Pope John XXIII: "Si altare sit ad orientem, versus populum …" ^[17]

The present rules regarding the Ordinary Form of the Roman Rite liturgy declare a free-standing main altar to be "desirable wherever possible." ^[18] Similarly, in the Anglican Communion, the rubrics of the Book of Common Prayer assumed an altar fixed against the wall, until Prayer Book revision in the twentieth century removed language which assumed any particular form of altar.

Altar and reredos from University Church, Dublin

As well as altars in the structural sense, it became customary in the West to have what in Latin were referred to as altaria portatilia (portable altars), more commonly referred to in English as "altar stones". When travelling, a priest could take one with him and place it on an ordinary table for saying Mass. They were also inserted into the centre of structural altars especially those made of wood. In that case, it was the altar stone that was considered liturgically to be the altar. The Pontificale Romanum contained a rite for blessing at the same time several of these altar stones.^[19] In the East the antimension served and continues to serve the same purpose. In the West, the obligation to use one for the celebration of Mass has not been encouraged.

The term "movable altar" or "portable altar" is now used of a full-scale structural altar, with or without an inserted altar stone, that can in fact be moved.^[20]

Such altars are found in Roman Catholic churches awaiting restructuring from an arrangement in which a priest celebrated Mass at a remote high altar, usually facing away from them, to one in which he is closer to the congregation and generally facing them. Both Catholic and Protestant churches use them to celebrate the Eucharist in places other than a church or chapel (such as outdoors or in an auditorium). In those Protestant churches in which the focus of worship is not on the Eucharist, which may be celebrated rarely, and in churches which want to make use of both a fixed and free-standing altar at different services, they are not only movable but are in fact occasionally moved. Churches that have adhered to the Protestant Reformation have favoured as altars free-standing wooden tables placed in the quire away from the east wall and the high altar, and without any altar stone.

Roman Catholic churches[link]

High altar of St. Michael's Church, Munich

The Eastern Catholic Churches each follow their own traditions, which in general correspond to those of similar Eastern Orthodox or Oriental Orthodox Churches. The rules indicated here are those of the Latin Church.

The Latin Church distinguishes between fixed altars (those attached to the floor) and movable altars (those that can be displaced), and states: "It is desirable that in every church there be a fixed altar, since this more clearly and permanently signifies Christ Jesus, the Living Stone (1 Peter 2:4; cf. Ephesians 2:10). In other places set aside for sacred celebrations, the altar may be movable."^[21]

A fixed altar should in general be topped by a slab of natural stone, thus conforming to tradition and to the significance attributed to the altar, but in many places dignified, well-crafted solid wood is permitted; the supports or base of a fixed altar may be of any dignified solid material. A movable altar may be of any noble solid material suitable for liturgical use.^[22]

The liturgical norms state:

It is fitting that the tradition of the Roman liturgy should be preserved of placing relics of martyrs or other saints beneath the altar. However, the following should be noted:

a) Relics intended for deposition should be of such a size that they can be recognized as parts of human bodies. Hence excessively small relics of one or more saints must not be deposited.

b) The greatest care must be taken to determine whether relics intended for deposition are authentic. It is better for an altar to be dedicated without relics than to have relics of doubtful credibility placed beneath it.

c) A reliquary must not be placed on the altar or in the table of the altar but beneath the table of the altar, as the design of the altar may allow.^[23]

This last norm explicitly excludes the practice customary in recent centuries of inserting relics into a specially created cavity within the table of an altar or altar stone. Placing of relics even in the base of a movable altar is also excluded.^[24]

"In building new churches, it is preferable for a single altar to be erected, one that in the gathering of the faithful will signify the one Christ and the one Eucharist of the Church. In already existing churches, however, when the old altar is so positioned that it makes the people's participation difficult but cannot be moved without damage to artistic value, another fixed altar, skillfully made and properly dedicated, should be erected and the sacred rites celebrated on it alone. In order that the attention of the faithful not be distracted from the new altar the old altar should not be decorated in any special way."^[25]

The altar, fixed or movable, should as a rule be separate from the wall so as to make it easy to walk around it and to celebrate Mass at it facing the people. It should be positioned so as to be the natural centre of attention of the whole congregation.^[26]

The altar should be covered by at least one white cloth, and nothing else should be placed upon the altar table other than what is required for the liturgical celebration. Candlesticks and a crucifix, when required, can be either on the altar or near it, and it is desirable that the crucifix remain even outside of liturgical celebrations.^[27]

Anglican churches[link]

The altar in St. Mary Anglican Church, Redcliffe, Bristol. It is decorated with a frontal in green, a colour typically associated with the seasons after Epiphany and Pentecost. Note the rood screen behind the free-standing altar.

Altars in the Anglican Communion vary widely. At the time of the Reformation, altars were fixed against the east end of the church, and the priests would celebrate the Mass standing at the front of the altar. Beginning with the rubrics of the Second Prayer Book of Edward VI published in 1552, and through the 1662 Book of Common Prayer (which prevailed for almost 300 years), the priest is directed to stand "at the north syde of the Table [altar]." This was variously interpreted over the years to mean the north side of the front of a fixed altar, the north end of a fixed altar (i.e., facing south), the north side of a free-standing altar (presumably facing those intending to receive the Elements who would be sitting in the quire stalls opposite), or at the north end of a free-standing altar placed lengthwise in the chancel, facing a congregation seated in the nave.

Often, where a celebrant chose to situate himself was meant to convey his churchmanship (that is, more Reformed or more Catholic). The use of candles or tabernacles were banned by canon law, with the only appointed adornment being a white linen cloth.