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Around 1200 Pope Innocent III (1198-1216) had the St. Peter's façade mosaic restores and also commissioned either the restoration or replacement of its apse mosaic. From the latter only a few fragments are preserved, including the head of the donor pope. Drawings and paintings from the sixteenth and seventeenth century provide only a vague indication of what the composition looked like, so it is difficult to determine whether the Early Christian mosaic was essentially preserved under Innocent III or replaced by new work.
In 1605 Pope Paul V ordered the east end of old St. Peter's nave, the last section of the early Christian basilica still standing, destroyed to make way for the new church then under construction. Unlike his sixteenth-century predecessors responsible for earlier demolition campaigns at the site, Pope Paul V provided for the preservation of "memoriae" from the old church, as well as for detailed documentation of the structure "in pictura et scriptura."
The job of implementing these provisions fell to Giacomo Grimaldi, an Italian priest, writer, and archivist, whose drawings and descriptions have provided scholars ever since with some of the most detailed information known about the early Christian basilica. Grimaldi was also instrumental in creating a type of museum in the crypt under the new St. Peter's, known as the Vatican grottoes, consisting of painted views of the old church, as well as artifacts from its many altars and chapels.
The destruction of the nave began soon after the demolition order was announced and proceeded from west to east; the oratory of John VII survived until 1609. Just before it came down, Grimaldi had numerous fragments of the mosaic and sculptural decoration taken to the Vatican grottoes to be preserved and exhibited, where many of them remain to this day.
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