▁isolated ▁groups ▁of ▁F ris ians ▁e ke ing ▁out ▁a ▁living ▁along ▁the ▁changing ▁coast . ▁The ▁area ▁was ▁Christian ised ▁by ▁British ▁and ▁Irish ▁mission aries ▁around ▁the ▁ 9 th ▁century . ▁ ▁Starting ▁around ▁the ▁ 1 2 th ▁century ▁the ▁population ▁began ▁to ▁grow . ▁In ▁ 1 2 3 1 , ▁the ▁first ▁reference ▁to ▁Cat wij ck ▁appeared ▁in ▁the ▁records . ▁At ▁this ▁time ▁Kat w ijk ▁aan ▁Ze e ▁was ▁little ▁more ▁than ▁a ▁few ▁wooden ▁houses . ▁ ▁A ▁reference ▁to ▁a ▁fish ▁market ▁on ▁the ▁beach ▁appeared ▁in ▁the ▁records ▁around ▁ 1 5 0 ▁years ▁later . ▁In ▁ 1 3 8 8 , ▁the ▁fish ▁market ▁was ▁moved ▁from ▁Kat w ijk ▁aan ▁den ▁R ijn ▁to ▁Kat w ijk ▁aan ▁Ze e . ▁Kat w ijk ▁aan ▁Ze e ▁and ▁Kat w ijk ▁aan ▁den ▁R ijn ▁were ▁part ▁of ▁the ▁same ▁he er lijk heid ▁called ▁" Be ide ▁de ▁Kat wij ken ▁en ▁' t ▁Z and " ▁( or ▁something ▁similar ). ▁They ▁have ▁been ▁administr atively ▁joined ▁for ▁centuries . ▁ ▁In ▁ 1 5 2 0 ▁a ▁Roman ▁ru in ▁known ▁as ▁Brit ten burg ▁emer ged ▁from ▁the ▁sh ifting ▁s ands ▁on ▁the ▁beach ▁just ▁south ▁of ▁the ▁mouth ▁of ▁the ▁O ude ▁R ijn , ▁much ▁to ▁everyone ' s ▁aston ishment . ▁It ▁became ▁the ▁subject ▁of ▁a ▁number ▁of ▁prints ▁and ▁paint ings . ▁It ▁was ▁square ▁in ▁shape