The Porta Capena--Baths of Caracalla--Vigna Guidi--SS. Nereo ed Achilleo--SS. Sisto e Domenico--S. Cesareo (S. Giovanni in Oleo--S. Giovanni in Porta Latina)--Columbarium of the Freedmen of Octavia--Tomb of the Scipios--Columbarium of the Vigna Codini--Arch of Drusus--Porta S. Sebastiano--Tombs of Geta and Priscilla--Church of Domine Quo Vadis (Vigna Marancia)--Catacombs of S. Calixtus, of S. Pretextatus, of the Jews, and SS. Nereo ed Achilleo--(Temple of Bacchus, _i.e._ S. Urbano--Grotto of Egeria--Temple of Divus Rediculus)--Basilica and Catacombs of S. Sebastiano--Circus of Maxentius--Temple of Romulus, son of Maxentius--Tomb of Cecilia Metella--Castle of the Caetani--Tombs of the Via Appia--Sta. Maria Nuova--Roma Vecchia--Casale Rotondo--Tor di Selce, &c. The _Via Appia_, called Regina Viarum by Statius, was begun B.C. 312, by the Censor Appius Claudius the Blind, "the most illustrious of the great Sabine and Patrician race, of whom he was the most remarkable representative." It was paved throughout, and during the first part of its course served as a kind of patrician cemetery, being bordered by a magnificent avenue of family tombs. It began at the Porta Capena, itself crossed by the Claudian aqueduct, which was due to the same great benefactor,-- "Substitit ad veteres arcus madidamque Capenam," and was carried by Claudius across the Pontine Marshes as far as Capua, but afterwards extended to Brundusium. The site of the Porta Capena, so important as marking the commencement of the Appian Way, was long a disputed subject. The Roman antiquaries maintained that it was outside the present Walls, basing their opinion on the statement of St. Gregory, that the river Almo was in that Regio, and considering the Almo identical with a small stream which is crossed in the hollow about half a mile beyond the Porta S. Sebastiano, and which passes through the Valle Caffarelle, and falls into the Tiber near S. Paolo. This stream, however, which rises at the foot of the Alban Hills below the lake, divides into two parts about six miles from Rome, and its smaller division, after flowing close to the Porta San Giovanni, recedes again into the country, enters Rome near the Porta Metronia, a little behind the Church of S. Sisto, and passing through the Circus Maximus, falls into the Tiber at the Pulchrum Littus, below the temple of Vesta. Close to the point where this, the smaller branch of the Almo, crosses the Via San Sebastiano, Mr. J. H. Parker, in 1868--69, discovered some remains, on the original line of walls, which he has identified, beyond doubt, as those of the _Porta Capena_, whose position had been already proved by Ampère and other authorities. Close to the Porta Capena stood a large group of historical buildings, of which no trace remains. On the right of the gate was the temple of Mars: