This are the substructures of the premises which were occupied by kitchen, dining room and accommodations for guests of the
Emperor Diocletian in his elegant palace-villa. The entire upper floor part, together with vaults of this substructure were
used for the construction and upgrading of the surrounding houses, as well as the cathedral bell tower in the Middle Ages.
So it is now a part of the eastern substructures (basements) under the open sky.