▁the ▁Hospital ▁Bridge ▁in ▁Boston , ▁while ▁the ▁second ▁is ▁near ▁Cow bridge ▁Lock . ▁Both ▁carry ▁the ▁text ▁" CA ST ▁AT ▁B UT TER LE Y ▁ 1 8 1 1 " ▁stamp ed ▁into ▁the ▁g ird ers , ▁and ▁are ▁supported ▁by ▁g rit stone ▁pi ers . ▁V aux hall ▁Bridge , ▁a ▁third ▁example ▁of ▁the ▁type , ▁was ▁replaced ▁by ▁a ▁road ▁bridge ▁in ▁ 1 9 2 4 . ▁At ▁the ▁south ▁end ▁of ▁the ▁d rain , ▁Ma ud ▁F oster ▁sl u ice ▁surv ives ▁largely ▁in ▁original ▁condition , ▁although ▁some ▁alter ations ▁were ▁made ▁in ▁the ▁tw enti eth ▁century . ▁It ▁consists ▁of ▁three ▁elli pt ical ▁arch es , ▁with ▁gates ▁made ▁of ▁tim ber ▁and ▁iron ▁bind ings . ▁They ▁are ▁raised ▁and ▁lower ed ▁by ▁pul le ys ▁mounted ▁on ▁an ▁overhead ▁g antry . ▁The ▁entrance ▁lock ▁at ▁Anton ' s ▁G ow t ▁is ▁also ▁listed . ▁It ▁was ▁alter ed ▁in ▁ 1 8 4 8 ▁when ▁the ▁Great ▁Northern ▁Railway ▁Lincoln shire ▁loop ▁line ▁crossed ▁the ▁northern ▁end ▁of ▁the ▁lock . ▁ ▁N unn ' s ▁Bridge ▁is ▁the ▁first ▁bridge ▁to ▁cross ▁the ▁Hob hole ▁D rain ▁to ▁the ▁north ▁of ▁Hob hole ▁S lu ice . ▁It ▁has ▁a ▁span ▁of ▁, ▁and ▁when ▁ere cted ▁in ▁ 1 9 4 8 ▁was ▁the ▁first ▁pre - str essed ▁concrete ▁bridge ▁cast ▁in ▁situ ▁in ▁Britain . ▁L ▁G ▁M