Those that are improperly called "caves" actually represent the gap between the old Constantinian basilica and the current one: walking in the "caves" as you walk in what was the basilica built by the emperor and lasted until the sixteenth century.
The plant of the Vatican grottoes, which branch into niches, corridors and side chapels, is that of a three-nave church (the so-called old caves) with chapels that house the tombs of the popes; the semicircular apse of the church, with chapels and funeral monuments, (the so-called new caves) has the ideal center of St. Peter's Chapel, which corresponds, above the caves, the papal altar and the dome of Michelangelo, and, in the necropolis underground, the tomb of the Apostle Peter, the first Pope of Rome.
The Vatican grottoes are a suggestive monumental complex for the so many historical memories. In addition to preserving the tombs of several popes, the caves are rich in works of art from the ancient basilica.
Among the most important works of art preserved in the Vatican grottoes we must certainly remember the tomb of Pope Boniface VIII, by Arnolfo di Cambio. Also important is the tomb of Cardinal berardo eroli by Giovanni Dalmatian and fragments of frescoes attributed to Pietro Cavallini.
The sarcophagus of Junius Bassus, and the tomb of Pope Sixtus IV in bronze (created by Antonio Pollaiolo in 1493) are preserved in the St. Peter's Treasury Chamber (access to the right aisle of the basilica above).