The Romans greatly changed the face of Britain by their great engineering works. They drew broad roads from place to place, seldom turning aside to avoid forest or river. Their solidly-built causeways were carried across the marshy tracts, and pierced through the midst of the densest woods. Where the road went, clearings on each side were made, and population sprang up in what had hitherto been trackless wilderness. The Romans explored the remotest corners of Wales and Cornwall in their search after mineral wealth; they worked many tin, lead, and copper mines in the island, and exported the ores to Gaul and Italy. They developed the fisheries of Britain, especially the oyster fishery; not only did they prize British pearls, but the oysters themselves were exported as a special luxury to the distant capital of the world. They improved the farming of the open country so much that in years of scarcity the corn of Britain fed northern Gaul. In the more pleasant corners of the land Roman officials or wealthy merchants built themselves fine villas, with floors of mosaic, and elaborate heating-apparatus to guard them against the cold of the northern winter. Hundreds of such abodes are to be found: they clustered especially thick along the south coast and in the vale of Gloucester. Gauls, Italians, Greeks, and Orientals came to share in the trade of Britain, and at the same time many of its natives must have crossed to the continent, notably those who were sent to serve in the auxiliary cohorts of Britons, which formed part of the Roman army, and were quartered on the Rhine and Danube. But in spite of all this intercourse, the Celts did not become Romanized like the Gauls or Spaniards; the survival of their native tongue to this day sufficiently proves it. In all the other provinces of the West, Latin completely extinguished the old native languages. In the towns, however, the Britons often took Roman names, and men of note in the countryside did the same. Many of the commonest Welsh names of to-day are corrupt forms of Latin names: Owen, for example, is a degradation from Eugenius, and Rhys from Ambrosius, though they have lost so entirely the shape of their ancient originals. [Sidenote: =Britain harassed by barbarians.=]