 At the time , John was in south @-@ east England recruiting mercenaries in preparation for his war with the barons . Rochester blocked the direct route to London , which was also held by the rebels . According to Roger of Wendover , the rebels at Rochester were led by William d 'Aubigny , lord of Belvoir . Estimates of the size of Rochester 's garrison vary , with the chroniclers ' figures ranging from 95 to 140 knights , supported by crossbowmen , sergeants , and others . Hearing the news that the city was in enemy hands , John immediately rode to Rochester and arrived on 13 October . Royal forces had arrived ahead of John and entered the city on 11 October , taking it by surprise and laying siege to the castle . Rochester bridge was pulled down to prevent the arrival of a relief force from London . The siege that followed was the largest in England up to that point , and would take nearly two months . 
