Rebel armies led by Simon de Montfort and Gilbert de Clare entered the city and set about trying to capture the castle. Again the castle's defenders resisted, this time with a different outcome. After a week, the rebel armies raised the siege in the face of relief from Henry himself. The garrison did not surrender, and the castle suffered extensive damage that was not repaired until the following century. The castle saw military action for the last time in 1381 when it was captured and ransacked during the Peasants' Revolt. As Rochester Castle fell out of use its materials were reused elsewhere and custodianship relinquished by the Crown. The castle and its grounds were opened to the public in the 1870s as a park. At various points during the 19th and 20th centuries repairs were carried out. The castle is protected as a Grade I listed building and Scheduled Monument. Today the ruins are in the guardianship of English Heritage and open to the public. Castles were introduced to England by the Normans in the 11th century and their construction, in the wake of the conquest of 1066, helped the Normans secure their new territory. Rochester was an important city, built on the site of a Roman town at the junction of the River Medway and Watling Street, a Roman road. It has long been assumed that the first castle was located next to the river, just outside the south-west corner of the town walls. The conjectural site of the early castle later became known as "Boley Hill". Archaeologist Tom McNeill has suggested that these earliest castles in England may have been purely military in character, built to contain a large number of troops in hostile territory. 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.