The first fortifications on the hill where the Marienberg Fortress now stands date from a thousand years before Christ, when the Celts built one of their formidable ring fortresses on this prime defensive position.
The city itself grew in the 7th century as it became the seat of a Franconian lord and, eventually, a religious centre and a place of pilgrimage for the martyred St Kilian.
In the 12th century the first of the powerful bishops was elevated to the worldly rank of Prince Bishop (actually "Duke of Western Franconia") - an important step as that meant that church donations and tithes as well as regional taxes all flowed into the bishops' administration.
Würzburg had grown so powerful that it was considered the unofficial capital of the Holy Roman Empire - the wedding of Emperor Frederick I was held here, for example.