The Holy Trinity Church has a cross shaped plan with a dome. It is composed of the nave, narthex (entrance area) and the altar alcove. In the church many Byzantine architecture features have been skilfully used such as the inner organization of the space and the decorative and illuminative systems. These features, together with the pyramidal shape, forms and proportions give the church a picturesque appearance. The Byzantine architectural elements in the church have been combined with western architectural elements belonging to the same period.
Inside the church are two columns with reused capitals (thought to have been taken from classical ruins in the city). An inscription inside the church contains the name of Andronicus Paleologus (Governor of the province of Berat from 1302 to 1326), indicating that the church must have been built during the 13th or 14th century with his financial support.
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.