Even after Hadrian 's Wall was built in the second century a.d. , marauding bands from the north figured out a way to circumvent this formidable line of defense by launching their boats across the Solway Firth , landing on the coast of Cumbria south of the Wall , and attacking the Romans from behind .
Marauding bands managed to avoid Hadrian 's wall by boating across the Solway Firth .