Cathedral of Saint Domnius
Split Cathedral was built in the early 4th century as part of the complex of the Roman palace of Diocletian in Split. The building, which was originally an imperial mausoleum, was not dedicated to the church until the 7th century. In the 11th century, a bell tower was added and in the 17th century, the cathedral was enlarged by the construction of an apse in the choir. Consecrated as a cathedral at the turn of the 7th century AD, it is considered to be the oldest Catholic cathedral in the world that remains in use in its original structure. As part of the Diocletian's Palace, it is a World Heritage Site.