Via dell’Arco della Ciambella is a one-block street buried in the middle of Rome’s Historic Center, roughly midway between the Piazza della Rotonda and the Largo di Torre Argentina. It is rather unremarkable, except for two massive brick walls jutting out from the north side. If you look carefully behind the front of the buildings along the street, you will notice that they are part of a single circular wall, the remnants of the central drum of Rome’s first Thermae, the Baths of Agrippa.
Built towards the end of the first century BC during the rule of Augustus, the baths were part of a highly articulated composition of religious and civic structures that included the Pantheon (rebuilt by Hadrian at the beginning of the second century AD) some 200 m to the north, and the Temple of Minerva Calcidica, now buried under Santa Maria sopra Minerva around the corner. By the Middle Ages, that grand composition had been replaced by a dense residential fabric of more-or-less rectangular blocks. Via dell’Arco della Ciambella is one of the streets within that fabric, sitting pretty much on the east-west axis of the bath’s main hall. The remains of the hall show the beginning of an arch--its main entryway--that gives the name to the street.
(By the way, the word “ciambella” refers to an Italian doughnut-shaped pastry, a shorthand analogy to the circular hall of the baths.)