An altar (from Latin altare, ara) is a table on which the Eucharist is celebrated. In pagan and Jewish religion, the altar was a sacrificial table, and in the Catholic and Orthodox Churches, this is reflected in the view of the Eucharistic celebration as a re-enactment of the sacrifice of Jesus Christ.
The main altar of a church is known as the high altar.
The first Christian altars were wooden tables, often simply the kitchen table in the home where the faithful met. When the early Christians started building churches, the altars were instead of stone, which in modern times is the preferred material in most churches.
Originally, there was only one altar in each church, but for practical reasons more altars were added in many churches.
An altar in a Catholic church must have a relic underneath or imbedded. At first, the altars seem to have been free-standing, and the celebrant stood facing the congregation. This was changed, and the altars were placed against the east wall so that the celebrant stood with his back to the congregation. In recent times, many altars have been restored to the original practice. In Rome, both types may be found. The altar must be covered with a white cloth when Mass is celebrated.