Cryptoporticus

You see a long, wide passage whose walls are lined with marble and mosaics; its darkness is rather eerie despite the light streaming from the skylights above. You can't help shivering and glancing apprehensively over your shoulder as you remember what happened here on January 21, 41 CE.

The emperor Gaius, popularly known as Caligula, was trapped in this corridor and assassinated by members of his own Praetorian Guard, in a conspiracy with some high-ranking members of the Senate. Here's the way Suetonius (Gaius LVIII. 2-3) tells the tale:

alii Sabinum summota per conscios centuriones turba signum more militiae petisse et Gaio "Iovem" dante Chaeream exclamasse: "accipe ratum!" respicientique maxillam ictu discidisse. Iacentem contractisque membris clamitantem se vivere ceteri vulneribus triginta confecerunt; nam signum erat omnium: "repete!"

"Some say that the tribune Cornelius Sabinus, after the people around Gaius had been dispersed by some centurions who were in on the plot, asked for the watchword in the manner of the military. When Gaius answered 'Jupiter,' Cassius Chaerea shouted 'Accept your fate!' and as Gaius looked around he split his jaw with a sword thrust. As Gaius lay on the ground with writhing limbs and cried out that he was still alive, the others completed the deed with thirty wounds; for the watchword of all was: 'Strike again!'"

A narrow passageway branches off this larger one, leading up to the grand new palace complex built by the emperor Domitian.