One of the mosaic merchant signs, for an ivory trader
Ostia Antica, Italy – “located at the mouth of the River Tiber, Ostia was said to have been founded by Ancus Marcius, the fourth king of Rome, in the 7th century BC. A later inscription refers to the event [Anco Marcio regi quarto a Romulo qui ab urbe condita primum coloniam — deduxit]. However the most ancient archaeological remains so far discovered are no older than the 4th century BC. The most ancient buildings currently visible are from the 3rd century BC, notably the Castrum (military camp) and of a slightly later date are, the Capitolium (temple of Jupiter, Juno and Minerva). The opus quadratum, the walls of the original castrum at Ostia provide important evidence for the building techniques that were employed in Roman urbanisation during the period of the Middle Republic.
Although Ostia was probably founded for the sole purpose of military defense — since hostile armies could eventually reach Rome by water through the mouth of the Tiber River — in time the port became a very important commercial harbor.” excerpt from wikipedia
great collection of mosaic photos from Ostia Antica