Aya Trias Basilica was built in the early 6th century and destroyed during the Arab raids of the 7th century. It was then abandoned, and a small church and other buildings were built to the south. These buildings in turn were abandoned and destroyed around the 9th century. All memory of the basilica disappeared, until it was rediscovered by chance in 1957, when it was partially excavated.
What can be seen of the basilica today is an entrance atrium at the western end of the basilica, (the end furthest away from today's entrance gate). This leads to an entrance lobby, or narthex, spanning the width of the basilica. This in turn leads to a three-aisled nave, with a number of columns still standing. here you can see the remains of a chancel. There is a large central apse and two smaller apses to the north and south. To the southeast of the basilica, you can see the remains of a large cross shaped baptismal chamber, the largest known on the island. It is thought that the other structures you can see here are the remains of the Bishop's Palace.
The narthex and nave are extensively covered with mosaics, mostly geometric patterns. In the northern nave, however, there are some exceptions. In particular, a pomegranate tree, alongside a pair of sandals.
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.