For this the heavy arm of Severus lighted on them not long before his death; he penetrated into their own territory and compelled them to cede considerable tracts,[113] from which indeed, after the old emperor had died in 211 at the camp of Eburacum, his sons at once of their own accord withdrew the garrisons, to be relieved of their burdensome defence. [Sidenote: Caledonians and Scots.] From the third century hardly anything is told us of the fate of the island. Since none of the emperors down to Diocletian and his colleagues derived the name of conqueror from the island, there were probably no more serious conflicts in that quarter; and, although in the region lying between the walls of Pius and of Hadrian the Roman system doubtless never gained a firm footing, yet at least the wall of Hadrian seems to have rendered even then the service for which it was intended, and the foreign civilisation seems to have developed in security behind it. In the time of Diocletian we find the district between the two walls evacuated, but the Hadrianic wall occupied still as before, and the rest of the Roman army in cantonments between it and the headquarters Eburacum, to ward off the predatory expeditions, thenceforth often mentioned, of the Caledonians, or--as they are now usually called--the "tattooed" (_picti_), and the Scots streaming in from Ivernia. [Sidenote: Fleet.] The Romans possessed a standing fleet in Britain; but, as the marine always remained the weak side of Roman warlike organisation, the British fleet was temporarily of importance only under Agricola. [Sidenote: Garrison and administration in the 2d and 3d centuries.]