[Illustration: PLAN OF THE GRAVES SURROUNDING THAT OF S. PETER DISCOVERED AT THE TIME OF PAUL V. (From a rare engraving by Benedetto Drei, head master mason to the Pope. The site of the tomb of S. Peter and the Fenestella are indicated by the author)] There are eleven left: of which eight ornament the balconies under the dome; two, the altar of S. Mauritius, and one (reproduced in our illustration) the Cappella della Pietà, the first on the right. It is called the _colonna santa_ (the holy column), because it was formerly used for the exorcism of evil spirits. It was enclosed in a marble _pluteus_ by Cardinal Orsini, in 1438. [Illustration: The Colonna Santa] The walls of the church were patched with fragments of tiles (_tegolozza_) and stone, except the apse and the arches, which were built of good bricks bearing the name of the emperor:-- _Dominus Noster_ CONSTANTINVS AVG_ustus_. Grimaldi says that he could not find two capitals or two bases alike. He says also that the architraves and friezes differed from one intercolumniation to another, and that some of them were inscribed with the names and praises of Titus, Trajan, Gallienus, and others. On each side of the first gateway, at the foot of the steps, were two granite columns, with composite capitals, representing the bust of the emperor Hadrian framed in acanthus leaves. The accompanying illustration, which was copied from an engraving of Ciampini, shows the aspect of the interior in the year 1588. [Illustration: View of a section of the Nave of old S. Peter's (South Side).] It gives a fairly good idea of the decorations of the nave, in their general outline; but fails to show the details of Constantine's patchwork. His system of structure may be better understood by referring to another of his creations, the basilica of S. Lorenzo fuori le Mura, of which a section of the interior is illustrated on p. 135. The atrium or quadri-portico was entered by three gateways, the middle one of which had doors of bronze inlaid with silver. The _nielli_ represented castles, cities, and territories which were subject to the apostolic see. The doors were stolen in 1167, and carried to Viterbo as trophies of war. The fountain in the centre of the atrium was a masterpiece of the time of Symmachus (498-514), who had a great predilection for buildings connected with hygiene and cleanliness, such as baths, fountains, and _necessaria_.[81] The fountain is described in my "Ancient Rome," p. 286; let me add here the particulars concerning its destruction. [Illustration: Nave of San Lorenzo fuori le Mura.]