▁Vict rix ▁at ▁the ▁end ▁of ▁the ▁ 1 st   century ▁the ▁walls ▁were ▁re construct ed ▁in ▁sand stone , ▁and ▁building ▁work ▁continued , ▁with ▁inter ru ptions , ▁until ▁the ▁Roman ▁circuit ▁of ▁the ▁walls ▁was ▁completed ▁over ▁ 1 0 0   year s ▁later . ▁During ▁the ▁same ▁period ▁the ▁to wers ▁and ▁gates ▁were ▁re built ▁in ▁stone . ▁ ▁Rep airs ▁were ▁carried ▁out ▁on ▁the ▁walls ▁throughout ▁the ▁Roman ▁occupation . ▁ ▁Ch ester ▁was ▁ref ort ified ▁in ▁ 9 0 7 ▁by ▁ Æ th elf l æ d , ▁but ▁how ▁this ▁affected ▁the ▁walls ▁is ▁not ▁precisely ▁known . ▁ ▁The ▁north ▁and ▁east ▁Roman ▁walls ▁were ▁certainly ▁used ▁in ▁the ▁fort ification , ▁as ▁they ▁are ▁still ▁in ▁existence ▁today , ▁but ▁it ▁is ▁possible ▁that ▁they ▁were ▁extended ▁to ▁the ▁west ▁and ▁south ▁to ▁meet ▁the ▁River ▁De e . ▁ ▁The ▁full ▁circuit ▁of ▁the ▁walls ▁as ▁they ▁are ▁today ▁was ▁completed ▁by ▁the ▁end ▁of ▁the ▁ 1 2 th   century . ▁ ▁The ▁north ▁and ▁east ▁walls ▁were ▁extended , ▁the ▁west ▁and ▁south ▁walls ▁were ▁built , ▁and ▁the ▁to wers ▁and ▁gates ▁were ▁incorpor ated . ▁ ▁Only ▁the ▁north ▁and ▁east ▁walls ▁contain ▁to wers , ▁as ▁the ▁river ▁was ▁thought ▁to ▁be ▁a ▁sufficient ▁defence ▁on ▁the ▁southern ▁and ▁western ▁sides . ▁ ▁Rep air ▁of ▁the ▁walls ▁was ▁an ▁on going ▁problem ▁during ▁the ▁medieval ▁period , ▁and ▁at