Sacristy of Saint Peter's Basilica, Religious preparation space at Saint Peter's Basilica, Vatican City.

The Sacristy of Saint Peter's is a large free-standing building on the south side of the basilica, designed by Carlo Marchionni and completed in 1784. Two covered corridors on low arches link it to the nave, one leading to the Sacristy of the Beneficiaries, the other to the Sacristy of the Canons. Between them opens the Common Sacristy, roofed by an octagonal lead-covered dome with a lantern; pairs of columns beside the passages come from Hadrian's Villa.

Pope Pius VI commissioned Carlo Marchionni to build the present sacristy in 1776; the first stone was laid on 22 September 1776, after demolishing buildings around the Rotonda di Santa Maria della Febbre and the church of Santo Stefano degli Ungheri. Foundations were finished by early 1778 and the whole work, with a large canonica for the Vatican chapter, was completed in 1784 and inaugurated on 10 June. Earlier projects by Maderno, Bernini and Juvarra, whose 1715 competition-winning wooden model was never built for cost reasons, came to nothing.

The Sacristy of the Beneficiates, on the west side, has its own chapel; it once held the Eucharistic Tabernacle made by Donatello and Michelozzo in 1432-1433, now shown in the Museum of the Treasury. The altar of the Common Sacristy carries a nineteenth-century mosaic reproducing Caravaggio's Deposition.

The space is usually accessible only on special tours, since it remains a working area of the basilica. Check ahead of time when access is available, and wear appropriate clothing since this is a religious place.

The columns flanking the passages into the two sacristies were taken from Hadrian's Villa at Tivoli, while their capitals came from the stock of materials Bernini had gathered for the basilica's bell tower, demolished in 1646 for structural reasons.