[Sidenote: Claudian Aqueduct.] Not far from the Sessorium, and springing out of the angle of the wall close to the Porta Maggiore, a series of lofty arches begins which extends throughout the whole length of the Cælian Hill. This is a branch aqueduct of the Aqua Claudia, built by Nero to supply the Cælian and Aventine Hills at a higher level than the Aqua Marcia and Aqua Julia, on which they had previously depended for their supply. It passed over the road leading from the Porta Maggiore to the Basilica of S. Croce, and thence ran along the higher ground through the vineyards of the Scala Santa, whence it skirted the Via di S. Stefano, and, at the Arch of Dolabella, was divided into three branches, one of which crossed the valley to the Palatine, the second ran towards the edge of the hill over the Coliseum, and a third towards the Porta Capena. [Sidenote: Arch of Dolabella.] The arch of Dolabella stands a little to the north-west of the Piazza della Navicella, and spans the road leading down from thence into the valley between the Cælian and Palatine, formerly called the Clivus Scauri. The archway consists of a single arch of travertine, without any ornamentation, but carrying an inscription to the effect that Publius Cornelius Dolabella, when consul, and Caius Julius Silanus, when Flamen Martialis, erected the arch by order of the Senate. The consulship of this Dolabella falls in the reign of Augustus A.D. 10, and therefore the arch can originally have had no connection with the Neronian aqueduct. It is possible, however, as Becker and Reber suggest, that the arch may have been originally built to carry the Aqua Marcia and Julia, which, as we know from Frontinus, supplied the Cælian before the building of the Neronian branch of the Aqua Claudia.[121] On one side the Arch of Dolabella is still completely hidden by the brickwork of the Neronian arches, and the other side was probably covered in a similar manner until after 1670, as we find no mention of this arch in Donatus, who could not have omitted to notice it in his description of the Neronian aqueduct had it been visible in his time. [Sidenote: Navicella.] The marble representation of a ship, which stands now in the Piazza della Navicella and gives its name to the place, was probably a votive offering to Jupiter Redux, and there may be some connection between these and the Castra Peregrinorum, as having perhaps been the place where the troops employed on foreign service were quartered. An inscription seems to allude to this connection between the Temple of Jupiter Redux and the camp. [Illustration: Arch of Dolabella.] [Sidenote: Houses on the Cælian.]