For a long number of years the present Porta S. Sebastiano (Porta
Appia) was considered to be the Porta Capena. This error was
rectified after the stone which marked the first mile was found (1584)
in the Vigna Naro outside the present gate. From it one mile (one
thousand paces) was measured backwards, and the result was the
discovery of the exact site of the Porta Capena by Mr. J. H. Parker in
1868; but the excavations have been filled in. The remains consist of
the sill of the gate, with fragments of the jambs, and the pavement of
the Via Appia with the raised footpath on each side of it. The west
flanking tower of the gate is under the gardener's cottage. This was
reopened in 1877. The gate was crossed by the Aqua Appia (Frontinus),
which Juvenal mentions as dripping, and Martial as showering down
drops.
The Porta Capena is represented twice in the reliefs of Trajan built
on to the Arch of Constantine. In the days of Tullus Hostilius, B.C.
668, Horatius killed his sister outside this gate. "A tomb of squared
stone was raised for Horatia, on the spot where she fell" (Livy, i.
26).