Ostia was an ancient Roman seaport located near the mouth of the Tiber River in what is now the Lazio region of Italy. It was one of the most important ports of the Roman Empire and served as a gateway for trade and travel between Rome and the rest of the Mediterranean world. Ostia was founded in the 4th century BC and remained an important port until the 5th century AD, when it was abandoned due to silting of the harbor.