The original system of tracks radiating from Salisbury Plain was simple. They led, in radiating lines straight and curved, directly to the lower Thames, to the ports of the Channel, to the southern estuaries, to the north-east--that is, to the Wash--and to the north direct by the Cotswolds. But true cross communication was lacking to this set, and was provided by the great road from the Exe to the Humber, which still survives in the form of the Fosse Way. It runs throughout the whole of our history, from very long before the first records nearly to the present day, and is to-day traceable throughout, and used in many places as a hard road. This main track was one of the dominant factors in the character of English travel. It has decayed under modern conditions because its “potential” has gone. There is no driving power to-day urging travel from south-west to north-east, and it is only in partial experiments and the linking up of separate lines that even our railway system serves that end. But before modern times the Fosse Way played a very great part. For some reason there was a perpetual necessity for passing from the south-west--Devon and Dorset--to the north-east coast. Two permanent potentials, that between north and south and that between east and west, help to explain the Fosse Way. England has always tended to fall into two cross divisions--a northern and a southern one, separated at first by climate (the northern more rude, the southern more gentle), then by agricultural conditions, the northern far less peopled, the southern more peopled and more wealthy; and to an eastern and western division separated by type of landscape, to some extent by climate, always to some extent by soil, difference in race, emphasized whenever an invasion came from the Welsh lands on the one side or from the North Sea on the other. The Fosse Way broke both those cross divisions and was a sort of “reinforcement” (as they say in modern concrete), taking the strain of cross tension across the island. iv In this short sketch of what were in some cases certainly, in others only presumably, the original British main tracks we have to note three factors which have always determined travel in Britain: the centres of internal economic production, the ports, and the Channel crossings.