Until roughly 407 A.D., the Roman army kept garrisons as far north in Britan
as Solway Firth, with fairly consistent interaction between themselves and
their 'unruly' neighbors to the North, and West, of them. Of course, I
stretch the definition of 'Roman' army a bit, as by the 4th Century A.D., the
Roman army in Britain was entirely manned by British inhabitants. So....