SACRED STONE (*petra sacra*, *tabula sacra*; *gestatorium*, *itinerarius*, *viaticum*). — A square or rectangular slab (25 x 30 cm.) consecrated by the bishop and containing a recess for holding relics of holy martyrs; it serves as an altar for celebrating Holy Mass wherever there is no fixed consecrated altar.
It is called a portable or gestatorial altar because it can be moved from place to place, especially suited for travel (*altare itinerarium*, *altare viaticum*, *lapis itinerarius*); it is also called a super-altar because it is placed upon a non-consecrated altar, whether movable or fixed. The *Codex Iuris Canonici* (CIC), can. 1197, §§1-2, prescribes that it must be a single intact natural stone, large enough to contain the Host and most of the chalice. Its use began after Constantine’s time, when the altar in the church, previously movable, became fixed and it was no longer permitted to celebrate Holy Mass outside a consecrated altar. The earliest certain evidence in the West dates to the 6th century (from a letter of 511 addressed to two English priests who were going on mission to Brittany); but it may already have been in use, since the letter treats it as a well-known and necessary thing for celebrating Mass during travel. Later, St. Bede recounts how two St. Ewalds, missionaries among the Saxons, carried with them a table to serve in place of an altar.
In the first millennium, tables of stone or wood were used (e.g., the oak table covered with silver plates found in the tomb of St. Cuthbert at Durham, Ireland); often the *petra sacra* was inserted into the wooden table or framed in a wooden casing or box; sometimes it was very small, of porphyry, onyx, rock crystal, or even slate; the relics were placed between the stone and the surrounding wood or in the wooden box. The latter are no longer permitted today (authentic decree no. 3162 of 31 August 1867). In the Middle Ages the rectangular form was preferred, sometimes also oval or round; from the 15th century onward, the square form prevailed. The size varies from 48.5 x 36.7 cm. and 12.5 x 7.5 cm. (the smallest *petra sacra* is that of Egbert’s portable altar at Trier, measuring 2.4 x 2.4 cm.). St. Charles Borromeo prescribes 36 x 29 cm.; the rubric merely requires a size sufficient to hold the Host with most of the foot of the chalice. In the consecration of a fixed altar, relics were always included in the sepulchre; for portable altars, however, until the 13th century, there were no precise regulations. As signs of consecration, small crosses were inserted beginning in the 15th century.
Outside a church or oratory, whether public or semi-public, only those who possess the privilege may celebrate Holy Mass on a portable altar.