Church of St. Donat (originally St. Trinity) is the most valuable monument of pre-Romanesque architecture of the early Middle Ages (9th century) in Croatia and symbol of the city, and because of the particular shape of one of the most important of its kind in Europe.By type of construction, it follows the form of the castle church circular layout of early Byzantine to the Carolingian period. However, for its rough monumentality (height 27, and width of 22 meters), an unusual cylindrical form and double interior space, it is distinguished by originality, without any direct models.According to legend was built by the Zadar bishop St. Donat in the 9th century, and is mentioned in the 10th century in the famous work "On the administration of the state" by the Byzantine Emperor Constantine Porphyrogenitus. Originally it was dedicated to the Holy Trinity, and the name of St. Donat began to arise from the 15th century onward.