In the New Law the altar is the table on which the Eucharistic Sacrifice is offered. Mass may sometimes be celebrated outside a sacred place, but never without an altar, or at least an altar-stone. In ecclesiastical history we find only two exceptions: St. Lucian (312) is said to have celebrated Mass on his breast whilst in prison, and Theodore Bishop of Tyre on the hands of his deacons (Mabillon, Praef. in 3 saec., n. 79).
According to Radulphus of Oxford (Prop. 25), St. Sixtus II (257-259) was the first to prescribe that Mass should be celebrated on an altar, and the rubric of the missal (XX) is merely a new promulgation of the law. It signifies, according to Amalarius (De Eccles. Officiis, I, xxiv) the Table of the Lord (mensa Domini), referring to the Last Supper, or the Cross (St. Bernard, De Coena Domini), or Christ ( St. Ambrose, IV, De Sacram. xii; Abbot Rupert, V, xxx). The last meaning explains the honour paid to it by incensing it, and the five crosses engraved on it signify HIs five wounds.