ANTIMENSION. — It is the portable altar of the Greeks.
With the passage of time, the Latin Church adopted only other portable altars of stone, while the Greek Church made use of wood and even cloth, eventually using only the latter. Today the a. is commonly a rectangle (sometimes a square) of 0.40 x 0.60 meters, made of silk or even canvas, which has sewn into its rear part a small pouch containing relics, included by the bishop during the consecration. Its origin lies in the frequent need to celebrate the divine mysteries far from churches or in places lacking fixed altars; however, positive historical data are available only from the 8th and 9th centuries. In antiquity it was used only when the altar was not consecrated; today, instead, it is used indifferently on all altars. Outside of Mass, it remains on the altar folded in four: the priest unfolds it at the appropriate time during the celebration of the divine sacrifice according to rubrical prescriptions. Ordinarily it is consecrated during the ceremony of the consecration of the church, when the bishop, having washed the altar a second time with perfumed wine or rose water, dries it with the a., and then repeats the same action after having anointed the altar with sacred chrism. The a. thus consecrated must remain on the altar until seven Masses have been celebrated upon II. In case of necessity, they may also be consecrated at other times by the bishop or by a priest delegated for this purpose. Priests of another rite are forbidden to celebrate Mass on the a. (can. 823, § 2).