Before we arrive at the famous square, we first see the San Giuseppe dei Falegnami (Joseph of the carpenters) at the Via S. Pietro in Carcere.
Underneath this 16th century church is the infamous Mamertine prison otherwise known as Carcer Mamertinus. We descend a few steps at the ‘Joseph of the carpenters and find ourselves in the actual prison. The monks of the church of course did not forget to emphasise on their wall that the apostles Peter and Paul were kept prisoner.
A hole in the floor still shows that this space had a second room, namely the Tullianum. This was probably a water reservoir that dried up at around 300 BC. It was then converted into a dungeon.
Thankfully, we can now just take the stairs. Back then, the prisoners were simply thrown down the hole. They then just had one way out, as a dead body. The dead bodies were taken out through a door to the Cloaca Maxima and ended up in the Tiber. Next to the Gaul Vercingetorix, Peter was a prisoner here as well.
C. Sallustius Crispus (86 to 35 BC) described the dungeon in his De Catilinae coniuratione as follows:
“Est in carcere locus, quod Tullianum appelatur, ubi paululum ascenderis ad laevam, circiter duodecim pedes humi depressus. Eum muniunt undique parietes atque insuper camera lapideis fornicibus iuncta; sed inculta, tenebris, odore foeda atque terribilis eius facies est.
In English: If you go up a little towards the left there is a place that is called the Tullianum, twelve feet below the ground’s surface. It is enclosed on all sides by walls with a room above it that has a vaulted roof of stone. Neglect, darkness and stench make it ominous and repulsive to behold.”
Source : Wikipedia and Wikipedia English
An altar and a source have been preserved. This source arose spontaneously when Peter wanted to baptise his fellow-prisoners. Peter did escape this prison, but he was assisted by God who sent angels to set him free. The prison is now a chapel devoted to Peter. In the strofes of the Vatican we will encounter another fresco with the same subject as Raphaël, but this 16th century painter obviously did not take the old Mamertine prison as his model. Read more about the Mamertine prison here at Wikipedia.
We now walk up along the side of the Palazzo Senatori, the current city council building, to arrive at the Piazza del Campidoglio.