The Underground of the Basilica of San Nicola in Carcere: between ancient temples and the secrets of the Forum Holitorium

A few steps from the Theater of Marcellus, at the beginning of the Sant'Angelo district, stands a church that at first glance appears purely medieval. However, walking around it is enough to notice the ancient columns embedded in its walls: the Basilica of San Nicola in Carcere is built, literally, over and inside three temples of Republican Rome. And the most surprising part lies right beneath the floor.

For those looking for underground sites to visit in Rome away from the queues of major monuments, it is an ideal stop on cool or rainy November days: a cozy, covered route in the heart of the historic center.

Three Republican temples inside a church
The basilica incorporates the remains of three temples traditionally dedicated to Janus, Spes (Hope), and Juno Sospita. Archaeologists still debate which structure belonged to each deity, but the framework is clearly visible: ancient columns, podiums, and masonry have become part of the church's architecture.
It is one of the clearest examples of Rome's layering. Here, eras did not erase each other; they built upon one another, and Christian worship physically leaned upon ancient tradition.

What to see in the underground of San Nicola in Carcere
Descending below church level, you walk among the foundations of the temples and the narrow passages that once separated them—true alleys of ancient Rome. Along the path, you encounter small rooms that tradition interpreted as prison cells, giving rise to the name "in Carcere" (in Prison).
However, archaeological studies suggest another interpretation: it is more likely these spaces were tied to the commerce of the nearby market, perhaps money changers. The underground also preserves traces of subsequent funerary uses.
Opening times and guided tours may vary, so it is best to check opening hours and access details before going.

The Forum Holitorium: what to see around the basilica
The temples once stood in the Forum Holitorium, the ancient herb and vegetable market. Located close to the Tiber next to the Forum Boarium (the cattle market), it was one of the liveliest hubs of commercial Rome.
Emerging from the underground, the walk continues seamlessly. The Portico of Octavia and the streets of the Jewish Ghetto are just a few minutes away, spanning two thousand years of history in a few hundred meters.

Other secret sites under Rome
San Nicola in Carcere belongs to a network of sites that tell the story of the city hidden beneath what we see today. To continue exploring, on the Rome With View blog you can find the hidden "city" beneath San Giovanni in Laterano and the story of the Crypta Balbi and the hidden city in the heart of Rome.

An afternoon in lesser-known Rome
Guests staying at Rome With View can reach San Nicola in Carcere with a pleasant stroll through the historic center and dedicate an afternoon to it, perhaps alongside other secret spots in central Rome. Afterward, return to the warm comfort of your accommodation, just in time to admire the rooftops and domes lighting up as evening falls.