 According to the Domesday Book of 1086 , the Bishop of Rochester was given land valued at 17s 4d in Aylesford , Kent , in compensation for land that became the site of Rochester Castle . Of the 48 castles mentioned in the survey , Rochester is the only one for which property @-@ owners were reimbursed when their land was taken to build the castle . From the 11th century the castle @-@ guard was a feudal obligation in England . This often took the form of knights garrisoning castles for their lords for a set period . There is no comprehensive list of which castles were owed service in this form , but military historian Cathcart King notes that they seem to have been predominantly high @-@ status castles . Rochester 's castle @-@ guard consisted of 60 knights ' fees , marking it as a particularly important fortification . 
