But no northern road--whether leading as did the Watling Street to Chester, or bending round as did the Icknield Way north-east after passing the ford of the Thames, or taking the island in diagonal as did the Fosse Way, or leading from London to the Humber as did the Ermine Street, or up at last to the Wall as did the Maiden Way--none of these could have a principal importance until the Romans invented frontiers: frontier garrisons to be fed, and frontier walls to be defended. Before their time this northern portion of England, split by the barren Pennines, hardly cultivated, leading nowhere, could not have been a goal for our principal road. That must have run to the south of Thames, and must have led from the Straits to the districts of which I have spoken--Hampshire, the Mendips, the Wiltshire Hills, Devonshire, and Cornwall. 3. The west of the island contained its principal supplies of mineral. Lead indeed was found and exploited in the north, but perhaps not before the Romans, whereas the variety and the amount of the wealth in the valley of the Severn and the peninsula beyond gave all that region an economic preponderance over the rest of the island. Tin, an absolute necessity for the Mediterranean civilisation, was certainly found in Cornwall, though the identification of the Scilly Islands with the Cassiterides is doubtful. The Mendips formed another metallic centre, presumably richer than even the Devonian peninsula. Lead certainly came in early times regularly from these hills, and Gloucester remained till the Middle Ages associated with the tax on iron. 4. There is a fourth aspect of the matter: it is of a sort that history neglects, but it is one the importance of which will be recognised with increasing force if the public knowledge of the past is destined to advance. It is that powers mainly resident in the mind have moulded society and its implements.