king john used york castle extensively during his reign, using the keep as his personal quarters for his own security. the castle was kept in good repair during that time. during this period, the first records of the use of the castle as a jail appeared, with references to prisoners taken during john's irish campaigns being held at york castle. by the 13th century there was a well-established system of castle-guards in place, under which various lands around york were granted in return for the provision of knights and crossbowmen to assist in protecting the castle.