The aisled St. Mary's Church of square ground plan whose lateral walls have been preserved almost to their original height. The size of the church (11x 24 m) indicates a large population of the nearby castrum erecting this edifice in the 5th - 6th centuries.
The altar area is two steps higher and is divided from the church nave by a partly preserved triumphal arch. The altar basis is preserved in situ. The atrium of the basilica holds a small collection of stone monuments, exhibiting, among other, church finds, transennae, stone window grids.
The front part of the basilica and around it was the site of an Early Christian cemetery 300 m long, stretching as far as the southeastern corner of the castrum.
The beginning of the 9th century saw the renovation of numerous churches, among them St. Mary's. It was refurbished with new stone furnishing bearing the recognizable interlace pattern. The large pagan population must have caused missionary activities carried out by the Benedictines from the many monasteries. If not earlier, this is when the Benedictine monastery was founded stretching north and south of the church.
In the 13th century the basilica belonged to the Templars, but when their order was abolished in 1312, life in the monastery faded away.
Near this church, a smaller aisleless church dedicated to St. Peter was built whose floor was decorated by a tricolored mosaic.
References:The Church of St Donatus name refers to Donatus of Zadar, who began construction on this church in the 9th century and ended it on the northeastern part of the Roman forum. It is the largest Pre-Romanesque building in Croatia.
The beginning of the building of the church was placed to the second half of the 8th century, and it is supposed to have been completed in the 9th century. The Zadar bishop and diplomat Donat (8th and 9th centuries) is credited with the building of the church. He led the representations of the Dalmatian cities to Constantinople and Charles the Great, which is why this church bears slight resemblance to Charlemagne's court chapels, especially the one in Aachen, and also to the Basilica of San Vitale in Ravenna. It belongs to the Pre-Romanesque architectural period.
The circular church, formerly domed, is 27 m high and is characterised by simplicity and technical primitivism.