 Complete the following phrase:  Many castles, especially royal castles, were left to decay in the 15th century; Kenilworth, however, continued to be used as a centre of choice, forming a late medieval palace fortress. Henry IV, John of Gaunts son, returned Kenilworth to royal ownership when he took the throne in 1399 and made extensive use of the castle. Henry V also used Kenilworth extensively, but preferred to stay in the Pleasance, the mock castle he had built on the other side of the Great Mere. According to the contemporary chronicler John Strecche, who lived at the neighbouring Kenilworth Priory, the French openly mocked Henry in 1414 by sending him a gift of tennis balls at Kenilworth. The French aim was to imply a lack of martial prowess; according to Strecche, the gift spurred Henrys decision to fight the 