One of the best preserved ancient imperial residences is located in the city of Split. At the end of the 3rd century, in the bay of the peninsula 5 kilometres southwest of Salona, it was built by the Roman emperor Diocletian to spend his old age in it. He died there as well in 316. Diocletian's Palace is today one of the key monuments for the study of ancient imperial palaces.
With a rectangular floor plan, the residence was built on the model of a Roman military camp. Enclosed by large ramparts, the palace, in addition to the four main towers at the corners, had another 6 square towers and two octagonal towers each that protected all three land entrances. The main entrance was the double Golden Gate on the north side while the Silver Gate was on the east and the Iron Gate on the west. The palace also had a private sea entrance for the emperor - the Brass Gate - which could only be reached by boat. The east and west gates were connected by one of the two main streets, the cardo. The second main street, the decumanus, began at the main gate and led through the defensive courtyard, which housed the army and servants, to the imperial rooms to the south. The streets thus properly divided the palace into smaller quarters and merged in the centre of the palace where the main square opened to the south - the Peristyle, which was bordered by pillars connected by arches. From the square there was access to Diocletian's mausoleum, a monumental building with a brick dome and rows of pillars and wreaths, in which the busts of Emperor Diocletian and his wife Prisca were found. The building was later converted into a Christian church, making the mausoleum of the emperor the persecutor of Christians the oldest cathedral in the world. West of the Peristyle was a sacral space where a very well-preserved temple of Jupiter with a richly decorated vault was found. Like the mausoleum, with the arrival of Christians the temple was converted into a baptistery.
Even though the palace has not been completely preserved, its floor plan is known for Diocletian's cellars located below the palace itself. They were built to level the irregular terrain and carry the burden of the palace. Their floor plan is a copy of the floor plan of the palace. Although they were buried over time, today they have been cleaned and made available to the public.
With the demolition of Salona and the arrival of the exiled population at the beginning of the 6th century, the palace gradually began to turn into the core of a new city, today's Split.