4. De Mysteriis. A valuable treatise on the Mysteries, under which title St. Ambrose includes Baptism, with its complement, Confirmation, and the Eucharist. It is somewhat similar to the Catecheses Mystagogicæ of St. Cyril of Jerusalem, expounding the doctrine and ceremonies of these sacraments. On doctrinal grounds the authenticity of the work has been impugned by some modern writers, but there is no sufficient foundation for their arguments, as the teaching may be paralleled in many other passages of St. Ambrose. The date is not certain, but may be about a.d. 387.