In the town at the foot of Marjan, features cathedral St.Duje, the oldest cathedral in the world.

This octagonal building is located inside Diocletian's Palace, served as an imperial mausoleum, and in the 8th century, the building where the car wanted to destroy Christianity, became a Christian cathedral. The circular interior, under which there is a crypt, there are columns decorated with wreaths particularly filigree work, a richly decorated with front door is a copy of the Hellenistic style. The brick dome was visibly decorated with mosaics, while the hexagonal pulpit from the 13th The wear characteristics of late Romanesque architecture. Monumental wooden doors was made of nut wood, the work of Andrija Buvina from the 1214th year into 28 parts, framed with floral motifs and depicts scenes from the life of Christ. St.Duje, together with the palace complex are included in the UNESCO World Heritage List.

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St. Duje is the patron saint of Split. Split each year on the seventh of May marks the day of their patron Saint Duje Holy Mass and procession.
Certainly, I recommend you to visit Split on that date