determine the velocity of the water, it would be too imperfect to enable us to form a tolerable judgment of the quantity intended. The quinarius may have been of the diameter of a coin of that name, or it may have been the name of a liquid measure equal to five quarters of the _sextarius_, and the sextarius is about a pint; but then we want the time in which such a measure was supplied. According to Forcellini, and he quotes Frontino, a quinarius is a pipe of the diameter of five _quadrantes_, and a quadrans, on the same authority, is a quarter of a foot. This would be preposterous, and the ancient remains show, that on an average, the section of each watercourse could not have exceeded an area of ten square feet. A quinarius then is five fourths of something, this seems all that is certain. A circular opening, three-quarters of an inch in diameter, at the depth of four feet from the surface, which is maintained always to the same level, will emit fifty-one cubic inches per second.[5] Most of the aqueducts approach each other near the Porta Maggiore. The Aqua Virginis, which enters Rome near the Villa Borghese, and the Trasteverine ones being alone wanting, and the modern Acqua Felice may be added to the number. This last runs along the wall from that gate to the Porta San Lorenzo, and then leaving the wall, is seen directing its course towards the Certosa. I shall therefore conduct you to the Porta Maggiore, and then tell you what is to be seen of them beyond it; but before we arrive at the gate, especially if we go from St. John Lateran, we see considerable remains of a branch of the Claudian, built, as we are told, by Nero, to conduct the water to the Palatine; and a little before arriving at the gate, a lane leading to the church of Santa Croce runs under it, and we have full opportunity to examine. It is of beautiful brickwork, at least the facings are so, and is meant for a gateway, since it is composed of one large arch in the middle, and two small arches, one over the other, on each side; and there have been architectural ornaments. The ancient watercourse runs at the top, above these upper arches; but there is one at present, suspended as it were in the upper part of the large arch, and passing at the bottom of the upper side arches, which I suppose to be a branch from the modern Acqua Felice; at least it is only from that, that it can now obtain its water. I have already mentioned to you the remains connected with the wall near the Porta Maggiore, as seen from the inside of the city; the three channels which pass over the gate, and the four which enter the wall on the left as you go out of the gate. The lowest and most ancient, the Aqua Appia enters the city, according to Piranesi, a little to the right of the gate, and winds over the Aventine; but it is almost everywhere buried, nor have I seen it in any one place at Rome, unless it be the lowest of those at the Porta Maggiore, as Piranesi’s plan seems to