The umbilicus, which was supposed to mark the centre of Rome, and of the Roman World, is known to us only from relatively late sources; the 4th century Regionary Catalogue (CodTop I, p. 174) and the 8th century Einsideln Intinerary (CodTop II, pp. 177, 191, 195). The former places it between the Temple of Concord and the Temple of Saturn, while the latter has it near the church of SS. Sergius and Bacchus. On the strength of these two indications, the Umbilicus Romae is identifiable with a three tiered brick cylinder, which stands at the northern end of the Hemicyclium of the Rostra. It is an early 4th century structure, but is later in date then the Tetrarchy monument of A.D. 303 (s. Basis Decennalia I, p.198). The brick structure may have been crowned by a circular aedicula, dating from an earlier period, travertine fragments of which have been found in the immediate vicinity. The monument was discovered in 1803, during the isolation of the Arch of Septimius Severus.
A podium, 13 m. square, surrounded by a double enclosure, was discovered on the south side of the Column of Antoninus Pius, when the latter was excavated in 1703 (s. Columna Antonini I, p.270). The enclosure was entered from the north, on the side facing the column. Francesco Bianchini took part in the excavations, and produced a detailed account of them (RM IV, 1889, pp. 49-59). He identified the complex as the Ustrinum for the funeral pyres of Faustina and Antoninus Pius. It was surrounded by an inner wall, and an outer balustrade, both constructed in travertine. A similar edifice, with identical measurements, came to light during the construction of the new Parliament building, in 1907, between Piazza del Parlamento, Via della Missione and Via dell'Impresa. Marble blocks from the central podium, together with various architectural fragments, were removed to the Museo Nazionale Romano, while the monument itself, still not fully excavated, disappeared in the foundations of the new Chamber of Deputies. It is likely to be the Ustrinum of Marcus Aurelius.