"An officer who is charged with the care of the sacristy, the church, and their contents. In ancient times many duties of the sacristan were performed by the doorkeepers (ostiarii), later by the mansionarii and the treasurers. The Decretals of Gregory IX (lib. I, tit. xxvi, "De officio sacristæ speak of the sacristan as if he had an honourable office attached to a certain benefice, and say that his duty was to care for the sacred vessels, vestments, lights, etc. Nowadays the sacristan is elected or appointed. The "Cæremoniale episcoporum" prescribed that in cathedral and collegiate churches the sacristan should be a priest, and describes his duties in regard to the sacristy, the Blessed Eucharist, the baptismal font, the holy oils, the sacred relics, the decoration of the church for the different seasons and feasts, the preparation of what is necessary for the various ceremonies, the pregustation in pontifical Mass, the ringing of the church bells, the preservation of order in the church, and the distribution of Masses; and finally it suggests that one or two canons be appointed each year to supervise the work of the sacristan and his assistants.
"The under-sacristan (custos) is also mentioned in the Decretals (lib. I, tit. xxvii, "De officio custodis"). He was the assistant of the sacristan, was subject to the archdeacon, and discharged duties very similar to those of the sacristan. Now the office is hardly ever attached to a benefice, but is usually a salaried position. The Council of Trent desired that, according to the old canons, clerics should hold such offices; but in most churches, on account of the difficulty or impossibility of obtaining clerics, laymen perform many of the duties of the sacristan and under-sacristan."