The suppression of the Celts was a hard enough job, it tasked the Roman legions to the utmost. Frightened by its scope, the Romans must have decided to think twice before they violated the Celtic people's rights too impudently.
All this while the Romans kept pushing on; at the end of the 1st c. A.D. when Agricola was the chief Roman governor of Britain (78-85 A.D.), he invaded Caledonia and in the battle of Mons Grampius defeated the chief oi the Picts, Galgacus. However, the Picts of Caledonia must have produced a strong impression upon the Romans, for in 121 A.D. the Emperor Hadrian caused a wall to be erected from the Tyne to the Solway Firth, that is in a line cutting through what is Newcastle today. They had erected another wall somewhat earlier, nearer south, so Hadrian's wall was a step further to the North. From the Forth to the Clyde the wall of Antonine was built (140 A.D.), later called Grime's Dyke.
Ireland was in those days inhabited by the Scots (some of the Scots must have migrated in their fight against the Romans later) in the 4th c.
The Romans made no attempt to subdue Ireland; as to Wales, it belonged to the so-called military districts of Roman Britain together with the other mountainous areas of the north and west (as opposed to the civil districts of the east and south where the greater part of the large towns were located).
The mountainous parts must have seemed prohibitive, inhabited as they were by those disobedient Celts who had retreated there to retain their independence; the same applied to Cornwall, or West Wales as it was called.
So forts were built at Carleon, Chester and York with a legion in each to ensure the safety of the occupation zone where the towns were restored and walled with ditches supplementing the protective power of walls. Thus, for instance, the wall around Londinium built after the Boadicea fright, was about 2 and a half metres thick at the base. London was made an inland port and lively trade was concentrated there since Roman Britain exported grain for the needs of the metropolis and of other Roman provinces as well, skins of wild and domestic animals, tin, pearls - and slaves, too.
London's position was especially fortunate for it was a centre of both external and internal trade: the Romans built roads leading to the garrison towns, for they couldn't have kept the country without reliable and efficient means of transportation. Three of those roads converged upon London making it a veritable commercial centre (not administrative centre, however, for though it was by far the largest of the towns, it was not given the Roman municipium status).
There were four principal roads: Ermine Street, leading to Lincoln and York (from York a special road led to Hadrian's Wall); Watling Street from London to Chester; Icknield way connecting London with Cirencester, Gloucester and Caerleon in South Wales, and the Fosse way that passed through the Cotswolds and connected Lincoln with Exeter, the extreme south-western Roman fort.
The roads were certainly an improvement on an otherwise impassable territory (though, of course, they made it accesible for numerous future invaders); the extensive cleared areas along the roads and rivers as well as the general improvement on agriculture that the rapacious Romans introduced using the cheap or practically free provincial labour - all that was no doubt beneficial for Britain's agricultural development.
There's something to be said for the cultural influence as well: Christianity was a step forward as compared to the heathenish Druidical rites; there was a handful of Latin words to enrich the Celtic vocabulary. There were some brutal laws that stayed on after the Romans left, chiefly concerned with the institution of slavery, such as the one mentioned by Mark Twain in his "Connecticut Yankee in King Arthur's Court", saying "if one slave killed his master all the slaves of that man must die for it," etc.
For the rest, the imported and therefore superficial civilization was never more than skin-deep with the country since it did not include the broad masses of the people to whom it was alien, so it evaporated as soon as the importers left, which happened four hundred years after they came.
Those historians who base their observations on the data derived from town life, that is, the life of the romanized upper layers of the British Celts, state that Romanization was completed and the Celts forgot they were Britons.
Romanization was nearly non-existent in Ireland and Scotland. In the countryside, the old Celtic way of life was preserved, the Celts continued living in their old Celtic way, suffering from the invaders' exploitation, passing their native customs andtraditions from generation to generation and speaking their Celtic dialects enriched by some of the Latin words like "castra" - military camp (found now in names like Lancaster, Winchester, Chichester, Cirencester, Leicester, Chester, etc.), "vallum"- wall (Hadrian's Wall, Anto-nine's Wall), "via strata" - street (Wailing street, Ermine street}. True, the wealthy British farmers had their lands tilled by slaves in the Roman fashion while the old Celtic social structure of the village coexisted with these imported arrangements.
The decay of Roman power in Britain became apparent already at the end of the 4th c.; the attacks of the wild Celtic tribes from behind the walls that had sealed off those dangerous areas, were no longer so efficiently and promptly repulsed in the latter part of the 5th c. as it used to have been the Romans' way; the usual grain-laden ships were no longer sent to the metropolis. Finally in 407 orders came for the legions to return. Evidently, the safety of Rome itself was in question: its rotten economy based on the sand of slavery, its greed-swollen conquest craze that lured the Romans on to bite off more than they could chew, its clay-legged military dictatorship aggravated by the bickerings of the would-be emperors who were constantly at each other's throat in their scrambling for power, made the great city an easy prey to any west-migrating barbaric tribes like the Germanic tribes of the period. As it is, there are supposi-tions to the effect that the British Roman ruler of the time, Constantine, was himself eager to try and get the crown for himself, using the legions at his disposal for the purpose. So the Romans left, and failed to return.