ALTARS
According to the best authorities the word altar is formed from the Latin altus, high, and ara, a mound or elevation. It is the sacred table upon which the Holy Sacrifice of the Mass is offered.
According to rule it ought to be about three and a half feet high, three feet wide, and six and a half feet long; and to denote the perfection of our Lord, whom it is made to represent in sacred symbolism, it should be solid throughout (Bouvry, ii. 223). Before Mass may be celebrated on it, it must first be consecrated by the bishop.
…
SACRED SYMBOLISM OF ALTARS
The precise symbolism of the altar is that it denotes Christ our Lord, in accordance with what St. Paul says in his first Epistle to the Corinthians: “They drank of the spiritual rock which followed them, and the rock was Christ” (Bouvry, ii. 222). According to Venerable Bede, the altar is the body of Christ, or all the saints in whom a divine fire ever burns, consuming all that is flesh.