Split's octagonal cathedral was built as Diocletian's personal mausoleum in the early 4th century — and is consequently one of the oldest cathedrals in the world, its core structure almost unchanged from its original form. The eight-sided exterior is lined with Corinthian columns and topped with a dome; the interior preserves Roman sarcophagi, medieval carved choir stalls, and a fine Romanesque portal.
The detached bell tower beside the cathedral is the city's most distinctive landmark, visible from the ferries arriving in harbour. The climb to the top (187 feet) gives the best view over the palace rooftops and the islands beyond. The tower was substantially rebuilt in the early 20th century after the medieval structure was found to be unstable; the current version is solid and the view worth the modest entrance fee.