The Bonn Minster (Bonner Münster) is one of Germany's oldest churches, having been built between the 11th and 13th centuries. At one point the church served as the cathedral for the Archbishopric of Cologne.
Castra Bonnensia was a fortress on the site of current Bonn built by the Romans in the 1st century AD. It survived the breakup of the Roman Empire as a civilian settlement, and in the 9th century it became the Frankish town of Bonnburg.
Around 235 AD, two Christian Roman soldiers stationed in Castra Bonnensia, Cassius and Florentius, were martyred for their faith. Tradition has it that a small memorial shrine was built over their graves in the 4th century by St. Helen, mother of Constantine. There is no surviving evidence of this first structure, but archaeological excavations have shown that the basilica stands on the site of a Roman temple and necropolis.
The original memorial hall was expanded into a larger church in the 6th and 7th centuries, and many people were buried near the martyrs inside and outside the building. Further extensions were carried out in the 8th century.
Around 1050 the church was demolished and construction began on the present Romanesque building, which dates from the 11th to 13th centuries. By the end of this period Bonn had grown in importance, becoming the capital of the Electorate and Archbishopric of Cologne, which was then a sovereign state. The new basilica appeared in the city's coat of arms. In 1643, Cassius and Florentius were officially declared the patron saints of the city of Bonn.
The basilica suffered significant damage in 1583-89, 1689, and in World War II, but each time it was fully restored. In 1956, the Bonner Münster was granted the status of Papal Minor Basilica.
The Broch of Gurness is an Iron Age broch village. Settlement here began sometime between 500 and 200 BC. At the centre of the settlement is a stone tower or broch, which once probably reached a height of around 10 metres. Its interior is divided into sections by upright slabs. The tower features two skins of drystone walls, with stone-floored galleries in between. These are accessed by steps. Stone ledges suggest that there was once an upper storey with a timber floor. The roof would have been thatched, surrounded by a wall walk linked by stairs to the ground floor. The broch features two hearths and a subterranean stone cistern with steps leading down into it. It is thought to have some religious significance, relating to an Iron Age cult of the underground.
The remains of the central tower are up to 3.6 metres high, and the stone walls are up to 4.1 metres thick.