The Vestibule

Entrance to Diocletian's Private Quarters

In ancient Roman architecture, the term "vestibulum" initially referred to the decorated space between the street and the front door of noble houses. In the late Republic period, the designation shifted to the passage area between the entrance and the atrium. The vestibule is an entrance hall located east of the peristyle, a circular building with an open dome above, serving as a transition between the peristyle and the private quarters of the palace.

The reason why the palace, constructed with brick, still stands today is explained in Friedrich Idam's podcast "opus cementitium," focusing on Roman cement