Resumen
Ostia Antica lies at the ancient mouth of the Tiber, about 25 km southwest of Rome. Tradition ties its foundation to Ancus Marcius in the regal period; the archaeologically visible city expands from a Republican castrum into a dense Imperial port town of warehouses (horrea), multi-storey apartments (insulae), mithraea, synagogues, and the famous Piazzale delle Corporazioni with mosaic emblems of trading guilds. Grain, oil, and marble moved through Ostia and later Portus to feed the capital.
As the coastline prograded and Portus took over shipping, Ostia declined; malaria and silting left standing brick walls that 19th–20th century excavations opened as an open-air museum. The site remains one of the richest laboratories for Roman domestic and commercial architecture. Pair with Pompeii and the Colosseum for complementary views of Roman urban life and spectacle.