In 1565 there were further clashes with Schwerin that which had far-reaching consequences. Among other things, the nobility introduced a beer excise that favoured the dukes. John Albert I advanced on the city with 500 horsemen, after Rostock had refused to take the formal oath of allegiance, and had the city wall razed (slighted) in order to have a fortress built. The conflict did not end until the first Rostock Inheritance Agreement of 21 September 1573, in which the state princes were guaranteed hereditary rule over the city for centuries and recognizing them as the supreme judicial authority; this bound Rostock for a long time. The citizens razed (or slighted) the fortress the following spring.