The French conquest of North Africa has shifted the southern frontier of Europe from the shores of the Mediterranean to the fringes of the Sahara. No longer is the sea a barrier between the continents; it has become a link. It may lash itself into a rage, but its rage is jeered at by the cable, the radio, the airplane, and the great steamers. The desert is now the true divide. And deeper and deeper into the desert the French outposts are being pushed, for the indomitable spirit of adventure—the spirit which led King Louis and his Crusaders to the Holy Land, Champlain to Canada and La Salle down the Mississippi, the armies of Napoleon to the Pyramids, which took Foureau down to Zinder, and de Brazza up the Congo, and Marchand to Fashoda—still runs hot and strong in the blood of France. Everywhere the Touareg raiders are being halted by the harsh “_Qui vive?_” of the French videttes. French well-drillers and agricultural experts are at work all the way from Libya to the Atlantic. The tribes of the far interior are becoming accustomed to the drone of the airplane and the panting of the motor-car. Twin lines of steel and festoons of copper wire have been flung far into the central wastes. The radio operators of Algeria gossip with their fellows at Lake Tchad and Timbuktu. France is striding southward in seven-league boots, carrying the frontier of civilization with her as she goes. In a much nearer future than most people dream of, her southern boundary will not be the Mediterranean, nor yet the Sahara, but the Equator. CHAPTER XI THE LAST HOME OF MYSTERY Tozeur, the ancient oasis town on the northern edge of the Grand Erg Oriental, is the jumping-off place for the desert; from here we were to plunge into the real Sahara. It was the end of the line, so far as Harvey and the Cadillac were concerned, and the day after our arrival he headed north again on the long detour, via Tunis and Constantine, to Biskra, in southern Algeria, where he was to await our arrival. For our journey across the trackless sand-wastes of the Grand Erg, where travel is entirely by compass and the sun, the officials of the Transat had placed at our disposal one of the curious twelve-wheelers designed by Renault, the great French automobile manufacturer, to solve the problem of transportation in the desert. The huge, cumbersome-looking vehicle, which in general appearance is a cross between a five-ton truck, a military reconnaissance car, and an overgrown station-wagon, deserves a paragraph or so of description, for it gives promise of playing as important a rôle in the conquest of the Sahara as the prairie-schooner did in the opening up of the American West.