Authorities on the subject say that the name and position of the third gate are lost.
Now we contend that the mass of ruins called the Scali Caci are the remains of the third gate, and that that gate was the Porta Carmenta, as distinctly stated by Virgil in his description of the meeting of Æneas and Evander, "without the gates." "Thus, walking on, he spoke, and showed the gate, since called Carmental by the Roman state; then stopping, through the narrow gate they pressed" (Virgil, "Æn.," viii.). The position corresponds with his description, and is just the spot where a gate would be required. The remains consist of two different early periods—immense blocks of soft tufa of the Arcadian period, and blocks of hard brown tufa of the time of Romulus, corresponding with the material of which his wall is built.
The Porta Carmenta was to the south, and is thus mentioned by Propertius (iv. 1):—
"Where rose that house of Remus upon tiers of steps, a single hearth was once the brothers' modest reign."
We suppose he uses the name of Remus here instead of Romulus on account of the rhythm.
Solinus gives this description of it:—
"It [Roma Quadrata] begins at the wood which is in the area of Apollo, and ends at the top of the stairs of Caius, where was [once] the cottage of Faustulus."
Plutarch says ("Romulus," xx.):—
"Romulus dwelt close by the steps, as they call them, of the fair shore, near the descent from the Mount Palatine to the Circus Maximus. There, they say, grew the holy blackthorn tree, of which they report that Romulus once, to try his strength, threw a dart from Mount Aventine, which struck so deep that no one could pluck it up, and grew into a trunk of considerable size, which posterity preserved and worshipped as one of the most sacred things, and therefore walled it about.
"But, they say, when Caius Cæsar was repairing the steps about it, some of the labourers digging too close, the root corrupted, and the tree quite withered."