The so-called Ardeatina postern is near the modern-day Via Cristoforo Colombo, the major road linking the city centre with the sea at Ostia, and is set into the walls in proximity to a corner tower.
When the Aurelian Walls were built, a small pre-existing brick gateway was incorporated into the exterior side of the fortification. The passageway originally consisted of an arch framed by two columns with Corinthian capitals and topped by an architrave and tympana. The type and style of the sophisticated terracotta decoration suggests that it dates to the 2nd century AD.
The transformation of the walls into a postern prompted significant changes: jambs and a travertine architrave were added to reduce the width of the aperture; the threshold was lowered, and the thickness of the arch was increased to accommodate a covered patrol walkway above.
In the 16th century the postern was walled up and was only reopened in 1940 during work to construct the Viale di Porta Ardeatina. A stretch of Roman paved road came to light at the same time; this too dated to before the walls and was identified as the Via Ardeatina associated with the original gateway. A tomb in travertine dating to the beginning of the 1st century AD was found Inside the circuit of walls, to one side of the postern. The remains are preserved in the nearby tower.
Scholars are not in agreement about the identification of the postern. Some hypothesize that the Via Ardeatina did not enter the city through this gateway, but further on, in the section of wall destroyed in 1538 to make way for the construction of the bastion.
5. Posterula Ardeatina, torre e sepolcro, prospetto interno.