This cathedral was originally built as Diocletian's mausoleum. The original octagonal form of the mausoleum, encircled by 24 columns, has been almost completely preserved. The domed interior is round with two rows of Corinthian columns and a frieze showing Emperor Diocletian and his wife, Prisca. The Romanesque belfry was constructed between the 12th and 16th centuries and reconstructed in 1908 after it collapsed. Notice the two lion figures at the foot of the belfry and the Egyptian black-granite sphinx dating from the 15th century BC on the right wall.

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