Located where the stream that drained the Forum Romanum ran into the Tiber in the early days of Rome, the Forum Borarium acted as the growing town's cattle market. The smell of the place was already legendary.
By the time of the Republic, the stream was incorporated into the Cloaca Maxima. The Forum Borarium, still the cattle market, was also the gateway to Rome for most goods shipped up the river. The principal docks of the city were just to the south, on the other side of the main city wall. This secondary role, as the first sight of Rome for many ship captains, lent the Forum Borarium a certain dignity; several important temples were built in it to increase its visual importance.
In the Imperial period, cattle were generally sold further outside the center of Rome. The Forum Borarium retained its name, but its functions were almost purely centered around its temples.
Two of those temples remain: a rectangular one dedicated to the river god Porticus, and a round one thought to be to Hercules the Victor. However, the location is more well-known as the home of the Bocca della Verita. Few of the tourists who stick their hands in the lion's mouth are aware of the history of the square they stand in.
Sources:
- Course notes from "The Topography and Monuments of Ancient Rome", taught at UC Berkeley by Professor Stephen Millar
- The Ancient Roman City, by John Stambaugh (course text)
- The Mute Stones Speak: the Story of Architecture in Italy by Paul MacKendrick (course text)