hadrians wall, northumberland national park, ruined stone arch and walls at milecastle 37, northern england, great britain

37 aelium ancient arch archaeological archaeology arches architecture attraction border borders britain britannia britannicus british britons building castle clouds cultural empire england europe excavation fort fortification fortlets foundations frontiers garrison gate grass grassy great hadrian hadriani hadrians heritage hiking history kingdom landscape limes masonry mile milecastle milefortlets national nature nestled nick northern northumberland park path pennines picts point post remains rigg roman rome scotland site square steel strategically structure trail travel uk unesco united vallum wall western world