During the first four centuries of Roman dominion in Britain, the spread of the manners and arts of the great mistress of the world followed close upon her success in arms; and the policy of one of the greatest of her generals, Agricola, bore fruit in the adoption of her civilization by the British provincials. The population clustered round the Roman stations, and cities sprang up, such as Chester, Bath, York, and Lincoln, between which a ready communication was maintained by the roads that still remain as monuments of engineering skill, and which, in many cases, have been used uninterruptedly from that time to the present day. Agriculture was carried on to such an extent, that Britain became one of the principal corn-producing regions of the Roman Empire; and a commerce with foreign countries was carried on from the ports on the banks of the Thames and the Severn (Gildas, i.). The mineral sources were also fully explored; tin was sought in the mines of Cornwall, lead in those of Derbyshire and Somersetshire, and iron in the forest of Dean, Sussex, and Northumberland. Nor was this material prosperity unaccompanied by the signs of luxury and culture. Numerous villas were dotted throughout the province, resembling in size and plan the quadrangle of a mediæval college at Oxford or Cambridge, and even in ruins astonishing us by their magnitude and the beauty of their tessellated pavements. York was the capital of the province and the centre of government, and consequently Yorkshire must have been, if anything, more completely penetrated with the Roman arts and civilization than any other part of Britain. The relation of the Roman conquerors to the conquered Celtic inhabitants was somewhat analogous to that which now exists between the English and the subject nations in India. Latin was the language spoken by the higher classes in the cities, of the army, and probably of the courts of law; while in the country the Celtic tongue held its ground, and still survives in the language of Wales. Christianity was probably professed in this country about the time of Constantine, and became the dominant religion by the middle of the fifth century, if not before.