The Porta Maggiore stood at the end of the long vista between the two great aqueducts, and was itself made out of two of the arches of the Claudian arcade, in the last of the angles that occurred at every half-mile. The penultimate one was at the eastern end of the Sessorium palace gardens, where this water entered Rome, and then, after passing the angle to the north, with the usual _piscina_ and _castellum aquæ_, or reservoir and filtering-place, turned again to the west, as far as that gate where the Claudian arcade terminated. From this point the Marcian turned to the north upon the great bank of earth which formed the outer defence of Rome in that part, and continued along it for another half-mile, as far as the Porta di S. Lorenzo, and beyond it to the Prætorian Camp; then turning again to the west, it went across the great inner foss between the outer bank, the great _agger_ of Servius Tullius, which formed the inner line, where remains of it were found near the railway station in 1871, with inscriptions on two of the _cippi_, stating that the three aqueducts passed there. It is not quite correct to say that the _arcades_ were carried there, because where the ground is high the _specus_ are carried underground. This is the case between the Porta Maggiore (the Porta Esquilina of Frontinus) and the Porta di S. Lorenzo (the Porta Viminalis of the same). The _specus_ is seen on arches close to each of the gates; but, between the two, it passed underground through a sort of hillock, about midway between the two gates, as is mentioned by Frontinus. The ground is high again near the Porta Chiusa at the Prætorian Camp, and in the great bank or _agger_ of Servius Tullius.