This little square by the river was the cattle market of the ancient city, and at the same time its oldest harbour, the place where ships came up the Tiber and livestock changed hands. Two temples still stand here, and they belong to the oldest buildings in Rome that never disappeared underground.
The round one is dedicated to Hercules and dates from the second century BC. It's the oldest marble building in the city still standing, and it survived because it became a church in the Middle Ages. The rectangular one beside it belonged to , the god of harbours.
The line of people on the other side is waiting for a drain cover. In the portico of the church hangs a marble disc with a bearded face and an open mouth, almost a metre and a half across, probably the cover of a drain that once belonged to a nearby temple. The Mouth of Truth is said to bite anyone who puts a hand in and tells a lie, a story that only arose in the Middle Ages and became world famous thanks to . The portico is free to enter, even if the queue for the photo doesn't tempt you.
From here it's two hundred metres back to the , past the , and that closes the loop.
Sources. Story: Sovrintendenza Capitolina ai Beni Culturali (Foro Boario, Tempio di Ercole Vincitore); Treccani (Bocca della Verità) Photos: Photo 1: Livioandronico2013 (Wikimedia Commons, CC BY-SA 4.0) | Photo 2: Sailko (Wikimedia Commons, CC BY 3.0)
