▁a ▁massive ▁red ▁brick ▁keep , ▁in ▁the ▁style ▁of ▁a ▁medieval ▁castle , ▁which ▁served ▁as ▁gun ▁tower ▁and ▁observation ▁post . ▁In ▁the ▁sides ▁of ▁the ▁tower ▁were ▁em bras ures ▁to ▁swe ep ▁the ▁d itch ▁with ▁fire . ▁The ▁dry ▁d itch ▁running ▁across ▁St ▁Margaret ' s ▁Street ▁was ▁crossed ▁by ▁draw bridge ▁through ▁a ▁substantial ▁cas em ated ▁guard house ▁in ▁the ▁form ▁of ▁an ▁arch ▁( which ▁was ▁demol ished ▁in ▁the ▁ 1 9 3 0 s ). ▁From ▁the ▁tower ▁ran ▁a ▁series ▁of ▁t unn els ▁to ▁the ▁out lying ▁guard h ouses . ▁Be hind ▁the ▁dry ▁d itch ▁running ▁from ▁the ▁tower ▁down ▁to ▁Ma id stone ▁Road ▁was ▁a ▁range ▁of ▁domestic ▁building ▁and ▁bar ra cks . ▁ ▁After ▁ 1 8 1 5 , ▁the ▁fort ▁served ▁a ▁variety ▁of ▁purposes , ▁including ▁military ▁prison ▁and ▁lun atic ▁as yl um . ▁After ▁nearby ▁Fort ▁Pitt ▁became ▁a ▁military ▁hospital , ▁the ▁patients ▁were ▁moved ▁from ▁Clar ence ▁to ▁a ▁new ▁as yl um , ▁although ▁the ▁prison ▁remained , ▁with ▁accounts ▁of ▁f log g ings ▁being ▁given ▁in ▁local ▁newsp apers . ▁The ▁fort ▁was ▁used ▁by ▁the ▁g arrison ▁art illery ▁throughout ▁the ▁First ▁World ▁War ▁as ▁a ▁rec ruit ing ▁centre . ▁After ▁the ▁war , ▁a ▁large ▁Territ orial ▁and ▁Vol unte er ▁Reserve ▁centre ▁was ▁built ▁alongside ▁the ▁site ▁and ▁the ▁main ▁bar rack ▁site ▁run ▁down . ▁During ▁the ▁Second ▁World