This stubborn resistance was backed too by natural obstacles of the gravest kind. Elsewhere in the Roman world the work of the conquerors was aided by the very civilization of Rome. Vandal and Frank marched along Roman highways over ground cleared by the Roman axe and crossed river or ravine on the Roman bridge. It was so doubtless with the English conquerors of Britain. But though Britain had long been Roman, her distance from the seat of Empire left her less Romanized than any other province of the West. Socially the Roman civilization had made little impression on any but the townsfolk, and the material civilization of the island was yet more backward than its social. Its natural defences threw obstacles in its invaders' way. In the forest belts which stretched over vast spaces of country they found barriers which in all cases checked their advance and in some cases finally stopped it. The Kentishmen and the South-Saxons were brought utterly to a standstill by the Andredsweald. The East-Saxons could never pierce the woods of their western border. The Fens proved impassable to the Northfolk and the Southfolk of East-Anglia. It was only after a long and terrible struggle that the West-Saxons could hew their way through the forests which sheltered the "Gwent" of the southern coast. Their attempt to break out of the circle of woodland which girt in the downs was in fact fruitless for thirty years; and in the height of their later power they were thrown back from the forests of Cheshire. [Sidenote: Withdrawal of the Britons]