They say when they are stricken with ague or fever, that they must have unwittingly slept on the site of an ancient habitation. Nor can the ground be cultivated near the ancient towns, because it causes fever; and thus it is that, as I have already stated, the present places of the same name are often miles distant from the former locality. No sooner does the plough or the spade turn up an ancient site than those who work there are attacked with illness. And thus the cities of the old world, and their houses and habitations, are deserted and lost in the forest. If the hunters, about to pitch their camp for the night, should stumble on so much as a crumbling brick or a fragment of hewn stone, they at once remove at least a bowshot away. The eastward flow of the Thames being at first checked, and finally almost or quite stopped by the formation of these banks, the water turned backwards as it were, and began to cover hitherto dry land. And this, with the other lesser rivers and brooks that no longer had any ultimate outlet, accounts for the Lake, so far as this side of the country is concerned. At the western extremity the waters also contract between the steep cliffs called the Red Rocks, near to which once existed the city of Bristol. Now the Welsh say, and the tradition of those who dwell in that part of the country bears them out, that in the time of the old world the River Severn flowed past the same spot, but not between these cliffs. The great river Severn coming down from the north, with England on one bank and Wales upon the other, entered the sea, widening out as it did so. Just before it reached the sea, another lesser river, called the Avon, the upper part of which is still there, joined it passing through this cleft in the rocks. But when the days of the old world ended in the twilight of the ancients, as the salt ocean fell back and its level became lower, vast sandbanks were disclosed, which presently extended across the most part of the Severn river. Others, indeed, think that the salt ocean did not sink, but that the land instead was lifted higher. Then they say that the waves threw up an immense quantity of shingle and sand, and that thus these banks were formed. All that we know with certainty, however, is, that across the estuary of the Severn there rose a broad barrier of beach, which grew wider with the years, and still increases westwards. It is as if the ocean churned up its floor and cast it forth upon the strand.