Among the best preserved remains of the Palace is the complex of ground vaults halls. The assembly, sometimes called the "basement hall," is built below the emperor's apartment, located in the southern quarter of the Palace. In order to equalize the soil inclination which descends from north to south, Diocletian’s builders built in the southern quarter of the assembly hall vaults whose only function was to support the upper floor, where is the emperor's residential complex. Because of these functions, the cellars are basically the same as the Diocletian's apartment.
By converting the Palace in Split, it destroyed the major part of the residential complex, but its ground floor halls as substructure are well preserved. Unlike the emperor's hall upstairs that were demolished and reconstructed medieval and later residential buildings and streets, the basement halls were now buried sewage and other waste materials of the medieval city, which was deposited in these areas for centuries, but their walls and vaults largely survived. The walls in the eastern part of the foundations are partially demolished because of removing the stones during the construction of the bell tower of the medieval cathedral.