Diocletian's Palace located in Split, Croatia was built during the turn of the century (4th century AD) during the time of the rule of Emperor Diocletian. Of course at that time Split did not exist, and the town that did exist then simply grew up around the palace. The reason the palace was built was so Diocletian could live there after he abdicated the throne in 305 AD. After the Middle Ages, the fancy palace remained pretty much unknown and forgotten until the ruins were surveyed by an architect who published a book on them. Robert Adam was a neoclassical architect and the palace book he published raised everyone's awareness of European architecture for the first time.
In 1979 UNESCO proposed that the inner city of Split built around the Palace and the Palace itself be included in the Wolrd Cultural Heritage registry. Then in 2006 Split city council gave approval to construct over 20 new building inside the palace (including a garage complex). This hasn't made too many people happy about using a World Heritage Monument for the monetary gain possible from the shops inside. Some say a monument is a monument and needs to be respected. Others argue for progress. In any event, your visit to the Palace will indeed be interesting.