Some topographers have identified the ruin in the Piazza di Pietra, now the Dogana, with the Posidonium, a portico built by Agrippa in memory of his naval exploits; but unless the ruin in the Piazza di Pietra be a later restoration after the fire of A.D. 80, which is possible enough, the style is not such as to allow us to assign it to the Augustan age. It has eleven fluted Corinthian marble columns supporting a tolerably well-preserved entablature, and plainly belonging to the longer side of a basilica or temple. The architrave, frieze, and cornice, have a heavy and unimpressive appearance, though some of the details of the work are rich and carefully executed. In the courtyard of the building a portion of the wall of the cella, and the spring of the arches of the vaulted roof, can be seen now incorporated into the modern building. Various conjectures have been made as to the name and history of this building. Some of the older topographers thought that it was the Temple of M. Aurelius, which seems, however, to have been nearer to the column of that emperor than the ruin in question is;[95] nor does the position of this ruin allow us to suppose that it formed any part of a series of buildings placed symmetrically round the column. Palladio gives an elaborate ground-plan, with all the details, and calls it the Temple of Mars; but there does not appear to be any evidence in favour of this appellation; nor is it known how much of Palladio’s design is taken from what remained of the ruin in his time, and how much is merely conjectural restoration. The conjecture of Urlichs that the Temple of Marciana, Trajan’s sister, stood here, rests on no evidence but that of the Notitia, and is rendered very improbable by the great size of the building, and by the fact that the expression in the Notitia is Basilica Marciani, and not Templum Marcianæ. Another hypothesis, which Professor Reber mentions, has more to recommend it. Antoninus Pius is said to have erected a temple in honour of his adopted father, Hadrian. This temple could not have stood in the Forum of Trajan, where there was no room left for such a building, and would most probably be placed near the rest of the Antonine buildings, not far from the Column of M. Aurelius. In the Mirabilia, the Temple of Hadrian is placed near the Church of S. Maria in Aquiro, which corresponded to the modern Chiesa degli Orfanelli; and part of a temple precinct built of travertine has been discovered in the Palazzo Cini, and is, perhaps, a relic of this temple. A medal of the year A.D. 151 contains a representation of the Temple of Hadrian, and corresponds tolerably well with the extant ruins; and in the neighbourhood of the Piazza di Pietra, several statues and fragments of inscriptions bearing the name of Antoninus Pius have been found at different times. When it is added that the style of building and execution of the ornamental work belong to the