A monumental court, called the Peristyle, formed the northern access to the imperial apartments. It also gave access to Diocletian's mausoleum on the east (now Cathedral of St. Domnius).

Split is best known for the ruins of the Palace of Diocletian (295-305 CE); collectively with the historic royal residences, fortifications, and churches in the city, the palace was designated a UNESCO World Heritage site in 1979. Diocletian built the massive palace in preparation for his retirement on 1 May 305 CE. It lies in a bay on the south side of a short peninsula running out from the Dalmatian coast, four miles from Salona, the capital of the Roman province of Dalmatia (and the birthplace of Diocletian). It is the world's most complete remains of a Roman palace. The ground plan of the palace is an irregular rectangle with towers projecting from the western, northern, and eastern facades. It combines qualities of a luxurious villa with those of a military camp, with its huge gates and watchtowers. The palace is enclosed by walls, and at times, it housed over 9,000 people. Subterranean portions of the palace feature barrel vaulted stonework.