 The castle built by Bishop Gundulf in the late 12th century was enclosed by a stone wall . Situated in the south @-@ west corner of the city , the castle used the remains of the Roman town walls as foundations . The circuit had at least one tower ; it was replaced in the 14th century . The original gateway was radically altered in the 13th or 14th century . From across the River Medway , the twin landmarks of Rochester 's castle and cathedral would have dominated the medieval landscape , symbolic of the authority of the church and nobility in the period . Most castles were built by secular nobles , but the work by Gundulf and his successor Corbeil provide examples of the role of the church in castle building . 
