Sextus Pompeius Festus probably lived in the later second century AD, perhaps at Narbo in Gaul. He wrote an encyclopaedic work (De verborum significatu, On the meaning of the words), containing a great variety of information.

De verborum significatu 214
Ostiam urbem ad exitum Tiberis in mare fluentis Ancus Marcius rex condidisse fertur; quod sive ad urbem sive ad coloniam quae postea condita est refertur. They say that Ancus Marcius founded the city of Ostia at the mouth of the Tiber where it flows into the sea; by this either the city is meant, or the colony that was founded later.

De verborum significatu 304
Quiritium fossae dicuntur quibus Ancus Marcius circumdedit urbem, quam secundum ostium Tiberis posuit, ex quo etiam Ostiam. [to be translated]