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.

Diocletian had this massive palace built to spend the last years of his life after abdicating on May 1, 305 AD. The bay is located on the south side of a short peninsula running out from the Dalmatian coast into the Adriatic, four miles from the site of Salona, the capital of the Roman province of Dalmatia. The terrain on which the palace was built slopes gently seaward. It is typical karst terrain, consisting of low limestone ridges running east to west with marl in the clefts between them. This palace is today the heart of the inner-city of Split where all the most important historical buildings can be found.

The importance of Diocletian's Palace far transcends local significance because of its level of preservation and the buildings of succeeding historical periods, stretching from Roman times onwards, which form the very tissue of old Split. The Palace is one of the most famous and integral architectural and cultural constructs on the Croatian Adriatic coast and holds an outstanding place in the Mediterranean, European and world heritage. In November 1979 UNESCO, in line with the international convention concerning the cultural and natural heritage, adopted a proposal that the historic Split inner city, built around the Palace, should be included in the register of the World Cultural Heritage.