After this we distinguish the external form of the Prætorian camp, and the wall is plain and without towers. In one place there are arches in the upper part, and traces of walls advancing at right angles. After this is a gateway stopt up, with one large scheme arch below, and six little arches above. Then comes the Porta San Lorenzo, built in the same style, perhaps by Aurelian, and repaired in 403, under _the most unconquered princes_, Arcadius and Honorius, as is recorded by an inscription. Within this is an arch of the aqueduct of the Aqua Marcia, repaired successively by Augustus, Titus, and Caracalla. There are stones disposed pedimentwise over the arch, and one of the ancient inscriptions runs horizontally across these stones. The walls continue to be of brick, with many towers, till we arrive at the angle by the Porta Maggiore, where some ancient aqueducts enter the walls. The Porta Maggiore is constructed of large blocks of travertine, and consisted anciently of two arches, as was usual in city gates, and three niches ornamented internally with cornices and pediments, one between, and one on each side of the entrances. It is supposed in the first instance to have formed part of an aqueduct, afterwards built up in the city walls; and if of five arches of an aqueduct three were filled up, and the two intermediate ones left open, a similar arrangement would result. Only one arch is now open, and the one which has been stopped up, does not seem to correspond exactly either in height or direction, with that through which the road passes. Two watercourses, the Anio novus and the Claudia, passed over it anciently, and the Acqua Felice has since been conducted through it. Three large inscriptions give due honours to Claudius, Vespasian, and Titus. Just to the north of this gate three other water-courses enter the wall of the city. The two upper are the Julia and Tepula, in rubble-work, which rest upon the constructions in peperino, of the Marcia. Another half buried, supposed to be the Anio vetus, is seen at the bottom. I hope in a succeeding walk to be able to give you some further idea of these aqueducts. To the right, as you issue from the gate, you find the wall made up of an ancient aqueduct, by filling up the arches; this is also observable on the inside, where, from the garden containing the temple of Venus and Cupid, you may trace a considerable portion of the different constructions. A little after leaving these aqueducts, you arrive at the remains of an amphitheatre, part of the circuit of which is built up in the walls; it consists of a range of Corinthian columns with arches between them, all of brick, and a small fragment of a second range; the brickwork is pretty well executed, but by no means equal to that of the temple of Rediculus. It is remarkable that the bricks of the arches are laid to a centre considerably lower than the centre of the curve. They are redder and longer than the others.