Between Provence and Dauphiné, dominating the cluse where the Durance flows, the Citadelle of Sisteron dominates the sky, crowning the town with its walls, bastions and keep. The view from here is breathtaking, stretching for 150 km and offering one of the finest vantage points in Haute Provence. It bears witness to eight centuries of architecture and history. The keep and sentry walk, built on the narrow rocky spine, date back to the 12th century. The tiered bastioned enclosures dating from the 16th century of the Vauban project, designed in 1692, only the powder magazine was built.
Major alterations were carried out on the north face in the mid-19th century. It was at this time that the magnificent underground staircase linking the fortress to the town was carved out of the rock.
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.