Waterford was established as a Viking port around 914. Its original city walls were extended by King John in 1210, making it Ireland's most powerful city. In the 15th century it resisted the forces of two pretenders to the English Crown, Lambert Simnel and Perkin Warbeck, and in 1649 defied Cromwell. In 1650 his forces returned and Waterford surrendered. Although the city escaped the customary slaughter, Catholics were either exiled to the west or shipped as slaves to the Caribbean, and the population dramatically declined.