“The country which now forms the circle of Swabia, had been left desert in the age of Augustus by the emigration of its ancient inhabitants. The fertility of the soil soon attracted a new colony from the adjacent provinces of Gaul. Crowds of adventurers, of a roving temper and of desperate fortunes, occupied the doubtful possession, and acknowledged by the payment of tithes the majesty of the Empire. To protect these new subjects a line of frontier garrisons was gradually extended from the Rhine to the Danube. About the reign of Hadrian, when that mode of defence began to be practised, these garrisons were connected and covered by a strong entrenchment of trees and palisades. In place of so rude a bulwark, the Emperor Probus constructed a stone wall of a considerable height, and strengthened it by towers at convenient distances. From the neighbourhood of Neustadt and Ratisbon on the Danube, it stretched across hills, valleys, rivers and morasses, as far as Wimpfen on the Neckar and at length terminated on the banks of the Rhine after a winding course of near two hundred miles. This barrier, uniting the two mighty streams that protected the provinces of Europe, seemed to fill up the vacant space through which the barbarians, and particularly the Allemanni, could penetrate with the greatest facility into the heart of the Empire. But the experience of the world, from China to Britain, has exposed the vain attempt of fortifying an extensive tract of country. An active enemy who can select and vary his points of attack must, in the end, discover some feeble spot, or some unguarded moment. The strength as well as the attention of the defenders is divided; and such are the blind effects of terror on the firmest troops, that a line broken in a single place is almost instantly deserted. The fate of the wall which Probus erected may confirm the general observation. Within a few years after his death, it was overthrown by the Allemanni. Its scattered ruins, universally ascribed to the power of the dæmon, now serve only to excite the wonder of the Swabian peasant.”[2]