Arca (or Arciila), a name applied to several ecclesiastical receptacles.
1. A chest intended to receive pecuniary offerings for the service of the Church or for the poor (Tertullian). Of this kind was probably the area pecunie, which pope Stephen (an. 260) is said to have handed over, with the sacred vessels, to his archdeacon when he was imprisoned; and also that which Paulinus Petricordius says was committed to the charge of a deacon chosen for the purpose.
2. It is used of a box or casket in which the eucharist was reserved. Thus Cyprian speaks of an "arca in which the sacrament of the Lord was," from which fire issued, to the great terror of a woman who attempted to open it with unholy hands. In this case the casket appears to have been in the house, and perhaps contained the reserved eucharist for the sick.
3. Among the prayers which precede the JEthiopic canon is one " Super arcam sive discum majorem." The prayer itself suggests that this area was used for precisely the same purpose as the paten (q.v.), inasmuch as in both cases the petition is that in or upon it may be perfected the body of the Lord. It may have served the purpose of an ANTIMENSIUM SEE ANTIMENSIUM (q.v.).
Its use was probably not limited to the case of unconsecrated altars. The Copts applied the term "mercy seat" to the Christian altar; and this area may have been an actual chest or ark, on the lid of which the mercy-seat consecration took place.