▁Sar um , ▁Ro chester ▁is ▁one ▁of ▁the ▁best ▁examples ▁of ▁a ▁closely ▁linked ▁castle ▁and ▁religious ▁building . ▁ ▁In ▁ 1 1 2 7 ▁King ▁Henry   I ▁granted ▁Ro chester ▁Castle ▁to ▁the ▁Arch bishop ▁of ▁Can ter bury , ▁William ▁de ▁Cor be il , ▁and ▁his ▁success ors ▁in ▁perpet u ity . ▁He ▁was ▁given ▁permission ▁to ▁build ▁" a ▁fort ification ▁or ▁tower ▁within ▁the ▁castle ▁and ▁keep ▁and ▁hold ▁it ▁forever ". ▁Cor be il ▁is ▁responsible ▁for ▁building ▁the ▁great ▁tower ▁or ▁keep ▁that ▁still ▁stands ▁today , ▁al beit ▁in ▁an ▁alter ed ▁state . ▁The ▁ 1 2 th   century ▁saw ▁many ▁cast les ▁in ▁England ▁re built ▁in ▁stone , ▁an ▁adv ancement ▁in ▁s oph istic ation ▁of ▁design ▁and ▁technology . ▁Ro chester ▁had ▁already ▁been ▁given ▁a ▁stone ▁cur tain ▁wall ▁by ▁Bishop ▁G und ulf , ▁and ▁the ▁keep ▁dates ▁from ▁this ▁period . ▁It ▁vis ually ▁domin ated ▁the ▁rest ▁of ▁the ▁castle , ▁tower ing ▁above ▁its ▁outer ▁walls , ▁and ▁acted ▁as ▁a ▁residence ▁containing ▁the ▁castle ' s ▁best ▁accommod ation . ▁A ▁st ur dy ▁fort ification , ▁it ▁could ▁also ▁serve ▁as ▁a ▁strong hold ▁in ▁the ▁event ▁of ▁military ▁action . ▁Such ▁was ▁the ▁importance ▁of ▁the ▁keep ▁as ▁a ▁symbol ▁of ▁Ro chester ▁it ▁was ▁dep icted ▁on ▁the ▁town ' s ▁se al ▁in ▁the ▁ 1 3 th   century . ▁ ▁Const ruction ▁progress