Which cathedral in Split incorporates the mausoleum built for the Roman emperor Diocletian?

The Cathedral of Saint Domnius in Split incorporates the mausoleum built for the Roman emperor Diocletian.

The cathedral occupies the former mausoleum within Diocletian’s Palace, constructed at the beginning of the 4th century in the Roman imperial residence at Split. After the palace became part of the medieval city, the mausoleum was converted into a Christian cathedral and dedicated to Saint Domnius, a bishop and martyr associated with the region.

Because of this transformation, the cathedral combines Roman imperial architecture with later Christian additions. Its original octagonal structure survives, while the entrance porch, bell tower, and other features belong to subsequent centuries. The bell tower was built mainly between the 13th and 16th centuries and later restored.

The building is sometimes called simply Split Cathedral. Its extraordinary age requires a distinction: the Roman mausoleum is ancient, but its use as a Christian cathedral began centuries after Diocletian’s death.