Nesactium was an ancient fortified town and hill fort of the Histri tribe. In pre-Roman times, Nesactium, ruled by its legendary king Epulon, was the capital of the tribal population of the peninsula called Histri, who were also connected to the prehistoric Castellieri culture. Some theories state a later Celtic influence, but who they were and where they came from has never been discovered for certain. It is believed that their main economic activities were trade and piracy all over the ancient Mediterranean Sea.
In 177 BC, the town was conquered by the Romans and destroyed. Rebuilt upon the original Histrian pattern, it was a Roman town until 46–45 BC, when the Ancient Greek colony Polai was elevated to Pietas Iulia, today Pula. The town was located on the ancient road Via Flavia, which connected Trieste to Dalmatia. The area was abandoned by the Romans in the 6th century, following the Slav invasions.
At the end of the fourth century, the walls were renewed. Two churches were added, next to each other, between the bathhouse and the forum. The southern one, the largest, was probably dedicated to Mary and used for the daily ceremonies; the northern one was used for baptisms and religious ceremonies. There are traces of fire, which may have something to do with the Avar attacks on Histria in 600 and 611.
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.