Originally the altar was the ordinary family table in house churches. Permanent altars, made of stone or marble, became popular only when the fixed altars of the Jewish Temple and pagan temples, with their animal sacrifices, no longer existed.
Early in Christianity altars became associated with martyrs; many churches and basilicas were built over their graves. This association was continued in the Middle Ages with the relics of martyrs placed in a bored-out hole in the top of the altar.
Altars stood in the middle of the sanctuary, with priests or bishop facing the people until the 5th century. Then it became popular for the altar and priest to face east, or toward the wall. The altar was moved against the wall, with the priest presiding with his back to the congregation.
Beginning in the Middle Ages, the altar could hardly be described as a table, becoming instead a display area for the relics, statues, paintings of saints, a crucifix, and finally the tabernacle itself. Shelves were built to hold candles and flowers.
In post-Vatican II times, the altar has once again become a recognizable table, close to the people, with the presiding priest facing the people and inviting their participation. Candles and the tabernacle are nearby, or the tabernacle is in a special chapel.