Diocletian's Palace is a building in Split, Croatia that was built by the emperor Diocletian the 3rd century AD. At the time it was built, there was no such city of Split, and the original town was built around the palace. The Latin name of the city, Spalatum, was derived from the original name Aspalathos, a white thorn common in the area. Contrary to the popular belief, it has nothing to do with the latin word for palace, palatium.

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 9000 people. Subterranean portions of the palace feature barrel vaulted stonework.

Water for the palace came from the Jadro River near Salona. Along the road from Split to Salona impressive remains of the original Roman aqueduct can still be seen. They were extensively restored in the 19th century.The British neo-classical architect Robert Adam surveyed the ruins of the palace and published Ruins of the Palace of the Emperor Diocletian at Spalatro in Dalmatia in 1764.