In Republican times Ostia was Rome's main commercial port and a military base defending the coastline and the mouth of the Tiber. The port continued to flourish under the Empire, despite the development, of Portus, a new port slightly to the northwest, in the 2nd century AD. Ostia's decline began in the 4th century, when a reduction in trade was combined with the gradual silting up of the harbour.
Then malaria became endemic in the area and the city, whose population may have been nearly 100,000 at its peak, was totally abandoned. Buried for centuries by sand, the city is remarkably well preserved. The site is less spectacular than Pompeii or Herculaneum because Ostia died a gradual death, but it gives a more complete picture of life under the Roman Empire.
People of all social classes and from all over the Mediterranean lived and worked here.