Tradition says that Ostia was founded by Ancus Marcius, the 4th king of Rome, who lived during the second half of the 7th century B.C., even if - till today - there is little archeological evidence corroborating such information. However, it seems that during the Regal period there was a built-up area near the mouth of the Tiber, where there were some salt marshes producing salt: a priceless and essential wealth. Salt was used to flavor and preserve food, so, keeping its production under control was absolutely necessary, as the historian Titus Livius says, recalling, among other things, that the whole area surrounding the mouth of the Tiber was strategically important for Rome.
In any case, the first settlement can be traced back to the beginning of the 4th century B.C., immediately after the defeat of the Etruscan town of Veio, situated on the right bank of the river, which fell to the Roman army in 396 B.C. Only at the end of that century a squared fortified post (castrum) was built. This castrum was surrounded by strong tufa walls and its main road axes - the Cardus and the Decumanus - were north-south oriented and east-west oriented, respectively. This military camp, called Ostia from the Latin word Ostium meaning "mouth of the river", was established at a distance of around 16 miles from Rome, as a military outpost to keep under control not only the access to the Tiber, but also its lower course and nearby areas, in order to defend Rome.
Ostia, the first Roman colony, became immediately a river port acquiring a commercial function to supply Rome with food stuff, particularly wheat, even if its strategic military function as naval base certainly prevailed.