Porta San Sebastiano is the largest and one of the best preserved of the gates in the defensive walls of the Aurelian Walls of Rome. The original name was Porta Appia because the Via Appia passed through it, the "regina viarum" which began a little further back, from the Porta Capena of the Servian walls. The current name derives from the proximity to the basilica and the catacombs of San Sebastiano. Of considerable interest, even if little known to most, is the figure of the Archangel Michael, engraved on the right internal jamb of the door. The archangel is represented while killing a dragon, and next to the image there is an inscription, in medieval Latin in Gothic characters, in which the battle fought on 29 September 1327 (St. Michael's day, in fact) by the militias is remembered. Roman Ghibelline dei Colonna led by Giacomo de 'Pontani (or Ponziano) against the Guelph army of the king of Naples Roberto d'Angiò, led by Giovanni Gaetano Orsini.
In the internal rooms of the door there is the small Museum of the Walls: the exhibition traces, through didactic panels, photos, models and casts of some decorative elements, the ancient, medieval and modern history of the Walls starting from those of the royal and republican age. of the VI-IV century BC, and then move on to the Aurelians . The itinerary includes a stop on the terraces and a pleasant walk along the covered walkway, which can be followed up to the arches of via Cristoforo Colombo.