Diocletian's Palace is an ancient fortress and palace complex located in the coastal city of Split, Croatia. It was built by the Roman emperor Diocletian at the turn of the 4th century AD and was intended to serve as his retirement home. The palace covers an area of about 30,000 square meters and includes a variety of structures, including residential quarters, a temple, a mausoleum, a defensive wall, and several gates.

Over the centuries, the palace has undergone numerous modifications and changes, with new structures being added and old ones being modified or demolished. Today, it serves as a major tourist attraction and a popular gathering spot for locals and visitors alike. The palace contains a mix of architectural styles, including Roman, Gothic, and Renaissance elements, and it is considered one of the best-preserved examples of Roman architecture in the world.

Some of the highlights of the palace include the Peristyle, a grand courtyard that was originally used for public gatherings and religious ceremonies; the Temple of Jupiter, a former Roman temple that now serves as a baptistery; and the Cathedral of St. Domnius, a medieval church that was built inside the palace walls. Visitors can also explore the palace's underground passages and cellars, which were used for storage and as a water supply in ancient times.

Diocletian's Palace was declared a UNESCO World Heritage Site in 1979 and is one of the most popular tourist destinations in Croatia, attracting millions of visitors each year.