The component parts of a fixed altar in the liturgical sense are the table (mensa), the support (stipes) and the sepulchrum. (See ALTAR-CAVITY.) The table must be a single slab of stone firmly joined by cement to the support, so that the table and support together make one piece. The surface of this table should be perfectly smooth and polished. Five Greek crosses are engraved on its surface, one at each of the four corners, about six inches from both edges. but directly above the support, and one in the centre. The support may be either a solid mass or it may consist of four or more columns. These must be of natural stone, firmly joined to the table. The substructure need not, however, consist of one piece, but should in every case be built on a solid foundation so as to make the structure permanent. The support may have any of the following forms:
• at each corner a column of natural stone, and the spaces between the columns may be filled with any kind of stone, brick, or cement;
• the space between the two columns in front may be left open, so as to place beneath the table (exposed) a reliquary containing the body (or a portion of the body) of a saint;
• besides the four columns, one at each corner, a fifth column may be placed in the centre at the front. In this case the back, and if desired the sides also, may be filled with stone, brick, or cement;
• if the table is small (it should in every case be larger than the stone of a portable altar), four columns are placed under it, one at each corner and, to make up the full length required, frames of stone or other material may be added to each side. these added portions are not consecrated, and hence may be constructed after the ceremony of consecration;
• if the table is deficient in width, four columns are placed under it, one at each corner, and a frame of stone or other material is added to the back. This addition is not consecrated, and may be constructed after the consecration of the altar.

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