The Piazza Navona was formerly a stadium, not a circus. The strongest evidence we have in favour of this rests on the shape of the piazza and of the ruins. One of the essential parts of a circus, the spina, is entirely wanting, and the end from which the runners started is at right angles to the longer sides, while in a circus, as in the case of the Circus of Maxentius, the carceres always stood in a slanting direction across the course, in order to equalise the distances round the spina. The obelisk, which now stands in the centre of the piazza was brought by Innocent X. from the Circus of Maxentius on the Appian Road. The Circus of Maxentius was not, however, its original site, for the hieroglyphics are of Roman execution and contain the name of Domitian. [Sidenote: Mausoleum of Augustus.] The northern part of the Campus Martius, between the Via del Ripetta and the Pincian Hill, contained only one great building of which we have any knowledge. This was the Mausoleum of Augustus, the ruins of which are now buried under the Teatro Correa, and are approached by a narrow entry leading out of the Via dei Pontefici. All that can now be seen of the shapeless mass which this once stately building presents, is a small part of the cylindrical brickwork basement on the left of the entrance to the Teatro Correa, and another fragment of the same at the back of the Church of S. Rocco. The proofs that these are the remains of the Mausoleum of Augustus are quite indisputable. Suetonius places it between the Tiber and the Flaminian Road, and Strabo speaks of it as standing near the bank of the river, descriptions which, though they are not very definite, agree with the site of the Teatro Correa sufficiently. Complete certainty is, however, afforded by the inscriptions which have been found on the site of the Ustrina Cæsarum, where the bodies were burnt before burial. These were found near the Corso, between the Via degli Otto Cantoni and the Via dei Pontefici, a spot answering to Strabo’s notice of the site of the Ustrina as standing in the middle of the Campus, which is here narrowed by the approach of the Pincian Hill towards the river. Augustus had built this magnificent tomb in his sixth consulship (B.C. 28). At that time the course of the Flaminian Road through the Campus was lined with the tombs of many eminent Roman statesmen and public characters, which have all, with the exception of the insignificant Tomb of Bibulus, totally disappeared. The modern city has entirely effaced all traces of these, but we may in all probability suppose that the Flaminian road presented no less striking a spectacle in the days of Augustus than the Appian, which we are accustomed to regard as the great burying-place of Rome.