Take the following as truth: 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.
Then the following statement: "Hadrian's Wall was build in the third century A.D." is true, false, or inconclusive?