<P> In Eastern Christianity (including the Eastern Catholic Churches) the use of stone, wood or metal is permitted . </P> <P> The usage of celebrating the Eucharist on the tombs of martyrs is by the Liber Pontificalis ascribed, probably mistakenly, to Pope Felix I (269 − 274). According to Johann Peter Kirsch the usage is likely to have preceded Pope Felix and to have concerned the celebration of Mass privately in the underground cemeteries known as the catacombs: the solemn celebration of the martyrs took place in the above - ground basilicas built over their place of burial . </P> <P> Within the catacomb crypts the Eucharist could be celebrated on a stone slab placed over the grave or sarcophagus of one or more martyrs within a space hollowed out of the tufa walls so as to form an arch - like niche . Both in the catacombs and in the above - ground churches the altar could also be a square or oblong block of stone resting on one or more columns (up to six) or on a masonry structure that enclosed the relics of martyrs . Instead of masonry, upright stone slabs could be used, thus forming, with the top slab, a stone chest containing the relics . This no doubt brought about both a change of form, from that of a simple table to that of a chest or tomb . </P> <P> Latin Church liturgy, before the reforms of the second half of the twentieth century, had complex rules about a distinction between a "fixed altar" and a "portable altar". The former term then meant an altar table (the top slab) with its supports, all of which had been consecrated as a single unit, while the latter term meant the (usually small) altar stone or any altar table consecrated separately from its supports . </P>

When did the catholic church turn the altar around