This opinion was already held by Palladio in the sixteenth century, but the Italian antiquaries since his time have adopted the most various hypotheses on the subject. There is, it is true, no actual proof that this was the temple of Mars Ultor, but there is strong presumptive evidence that it was so. The ‘Catalogue of the Curiosum’ places it next to the Forum Julium in the eighth region. Now the eighth region was bounded on the east, in this neighbourhood, by the Quirinal Hill and the Via del Sole, or a street a little to the east of it, and we are tolerably sure that the forum transitorium filled up a great part of the space between the temple in question and the above-mentioned street, and that the Forum Julium intervened between it and the Forum Romanum, while the Forum Trajani limits the space to the westward within which we can suppose the Forum Augusti to have been. Thus the only space left in the eighth region within which the Forum of Augustus can be supposed to have been contained, is that bounded by the Via della Croce Bianca, the Via del Priorato, and the Via di Tor di Conti. The ruins of the temple consist of three lofty fluted Corinthian columns, a pilaster of white Carrara marble, a part of the surmounting architrave, and the corresponding wall of the cella of the temple. Antiquarians are of opinion that the purity of style and elegance of these columns, and their ornamentation, forms a strong proof that they were designed and executed in the best times of Roman architectural art, and cannot belong to a period later than that of Augustus. The richest decorative work is to be seen under the roof of the portico, between the columns and the wall of the cella. [Sidenote: Exterior wall. Arco dei Pantani.] These three columns stood at the side of the temple which abutted on the exterior wall of the Forum, as the ruins show. A large portion of this wall is still standing on each side of the arch called the Arco dei Pantani. The arch itself is built of travertine, the wall of blocks of peperino laid alternately with the longer and shorter sides outwards as in the masonry of the tabularium. In the middle ages a door was fitted on to this archway, and a portion of the stone was cut away on the west side. This has injured its architectural beauty very much. It has also been stripped of the marble facing with which it was probably covered originally, and being now half buried in the rubbish of ages, it presents a somewhat mean and rough appearance. This archway formed one of the entrances to the Forum Augusti from the east. The wall of the enclosure can be traced for a considerable distance on each side of it, but there are no other archways now open. The monotonous appearance of so high a wall is relieved by having the edges of the stones cut so that each block stands out separately, and the lower part of the wall is divided into two, and its upper into three stages by projecting ruins of travertine.