Split’s octagonal cathedral is one of the best-preserved Ancient Roman buildings standing today. It was built as a mausoleum for Diocletian, the last famous persecutor of the Christians, who was interred here in 311 AD. The Christians got the last laugh, destroying the emperor's sarcophagus and converting his tomb into a church in the 5th century, dedicated to one of his victims. Note that a ticket for the cathedral includes admission to its crypt, treasury and baptistry (Temple of Jupiter).

The exterior of the building is still encircled by an original colonnade of 24 columns. A much later addition, the tall Romanesque belfry was constructed between the 12th and 16th centuries and reconstructed in 1908 after it collapsed. Notice the two lion figures at its base. Tickets are sold separately for those eager to climb up the belfry for views over the old town's rooftops.

Visitor access to the cathedral is via the sacristy, situated in an annex around the right-hand side of the building. This structure also houses the cathedral's treasury, which is rich in reliquaries, icons, church robes, illuminated manuscripts and documents in Glagolitic script.

Inside the cathedral itself, the domed interior has two rows of Corinthian columns and a frieze running high up on the walls which, surprisingly, still includes images of the emperor and his wife. To the left of the main altar is the altar of St Anastasius (Sveti Staš; 1448), carved by Juraj Dalmatinac. It features a relief of The Flagellation of Christ, which is considered one of the finest sculptural works of its time in Dalmatia.

The choir is furnished with 13th-century Romanesque seats, the oldest of their kind in Dalmatia. Other highlights include a 13th-century pulpit, the right-hand altar carved by Bonino da Milano in 1427, and the vault above the altar decorated with murals by Dujam Vušković. As you leave, take a look at the remarkable scenes from the life of Christ carved on the wooden entrance doors. Carved by Andrija Buvina in the 13th century, the scenes are presented in 28 squares, 14 on each side, and recall the fashion of Romanesque miniatures of the time.

Don't forget to take a look in the Cathedral crypt, an eerily quiet chamber which stays cool even on the hottest days. It's now a chapel dedicated to St Lucy.