As long as Gaul was not completely tranquillised, and stubborn tribes defended their hereditary liberties in the Alpine valleys, the Germans were treated with consideration. The imperator Augustus even confided the safety of his person and of the Capitol to a German troop of horse, as the divine Julius had done before him, and Vipsanius Agrippa settled the Ubii, who were hard pressed by the Suevi, on the left bank of the Rhine and founded the “Agrippine Colony,” the parent city of Cologne. Even the attack made by the eastern dwellers on the lower Rhine on the camp of M. Lollius, who had made an inroad into their territory because they had seized and crucified some Roman spies, went unpunished. But when the new division of Gaul into provinces had been accomplished, and the Alpine districts had been reduced to submission to the sway of Rome, Drusus the gallant and daring stepson of Augustus conceived the project of extending the borders of the empire beyond the Rhine and advancing further along the road which the great Cæsar had trodden. After providing for the protection of the river by strongly fortifying the ancient confederate towns from Basel (Augusta Rauracorum) to Cologne (Colonia Agrippina)--to wit, Strasburg (Argentoratum), Speyer, Worms, Mainz, Bonn, etc., and creating fresh bulwarks and _points d’appui_ both for defence and attack by founding the “Old Camp” (Castra Vetera) where Xanten now stands, and other castella, he next attempted to secure the northern districts. He induced the Batavians, who inhabited the marshy lowlands from the Rhine and Vaal to the North Sea, and their neighbours on the east, the Frisians, who occupied the seacoast as far as the Ems, to enter into friendship and alliance with the Romans; and then, by constructing a navigable canal which bears the name of “Drusus-Furt” to this day, he connected the lower course of the Rhine by means of the Yssel with the inland lake of Flevo, which at that time communicated with the sea by a navigable river of the same name, but which has since been widened out by the floods into an open bay, the Zuyder Zee. He then sailed into the German ocean with the fleet built on the Rhine, and, skirting the Frisian coast, came to the mouth of the Ems, where the legions fought some skirmishes with the Bructeri and Chauci. The fleet was here exposed to a great danger, for the ebb of the tide drew the waters of the channel away from the ships and left them high and dry. They were only saved from destruction by the aid of the Frisians who had accompanied the Romans by land with an army. When the incoming tide floated the ships once more Drusus returned to Batavia.