ung sh alle ▁built ▁directly ▁over ▁the ▁remains ▁of ▁the ▁settlement . ▁ ▁During ▁the ▁same ▁period , ▁the ▁construction ▁of ▁the ▁King ▁Ludwig ▁Main - Dan ube ▁canal ▁( 1 8 3 6 – 4 5 ) ▁through ▁the ▁Alt m ühl ▁river ▁valley ▁destroyed ▁the ▁surv iving ▁bits ▁of ▁the ▁northern ▁wall ▁as ▁well ▁as ▁any ▁evidence ▁of ▁the ▁water front ▁activities ▁the ▁settlement ▁had ▁engaged ▁in . ▁ ▁Description ▁ ▁Mich els berg ▁fort ifications ▁ ▁The ▁exterior ▁wall ▁of ▁the ▁late - C elt ic ▁opp id um ▁surrounded ▁the ▁whole ▁Mich els berg ▁and ▁Hir sch berg . ▁Inside ▁the ▁area ▁of ▁roughly ▁ 6 0 0 ▁ha ▁the ▁settlement ▁from ▁the ▁second ▁and ▁first ▁century ▁B CE ▁now ▁referred ▁to ▁as ▁Alc imo ennis ▁was ▁located . ▁It ▁is ▁the ▁second ▁largest ▁such ▁site ▁in ▁southern ▁Germany ▁after ▁He id eng ra ben . ▁The ▁settlement ▁included ▁an ▁art isan ▁quarter ▁at ▁the ▁Mit ter feld ▁and ▁a ▁vi ere ck sch anze ▁on ▁an ▁island ▁in ▁the ▁Alt m ühl . ▁Otherwise , ▁few ▁housing ▁units ▁or ▁gra ves ▁have ▁been ▁discovered . ▁The ▁opp id um ▁was ▁secured ▁by ▁at ▁least ▁three ▁section al ▁wall - and - mo at ▁def ences . ▁All ▁the ▁walls ▁followed ▁the ▁same ▁p f ost ensch l itz m auer ▁design : ▁tree ▁tr unks ▁of ▁roughly ▁ 6 0   cm ▁diameter ▁were ▁pushed ▁into ▁the ▁earth ▁at ▁least ▁ 1 ▁m ▁deep ▁and ▁roughly ▁ 2