The hardihood of the enterprise, unsuccessful as it was, seems to have alarmed the Germans. The tribes between the Rhine and Weser therefore entered into an alliance for the defence of their country against the enemy who menaced it. The Chatti refused to join this league, and their neighbours the Sugambri consequently went to war with them, just as Drusus, who had spent the winter in Rome, reappeared on the Rhine and crossed the boundary stream at the “Old Standing Camp” (at Xanten). He subjugated the Usipetes, and having made a bridge over the Lupia (Lippe), he traversed unopposed the country of the Sigambri, which was denuded of its fighting men, and attacked the Cherusci on the left bank of the Weser. Scarcity of provisions and the approach of winter forced him, however, to retreat. On his return march the Germans attacked him fiercely on all sides. Pent in a narrow gorge and hard beset, he and his army would have been irretrievably lost had not the Germans, thinking the enemy already vanquished, ventured upon the final massacre with savage eagerness and without any order or method. The victory of which they thought themselves certain passed over to Roman strategy. The Germans were beaten and had to look on while the Romans built the castellum of Aliso which they garrisoned and used as a _point d’appui_ for later undertakings. The emperor refused the title of imperator, by which the army hailed their general, but granted his victorious son an ovation and triumphal honours. [Illustration: DRUSUS (From a bronze in the Louvre Museum)] [Sidenote: [11-9 B.C.]] To secure a strong base for his campaigns of conquest Drusus, after a personal interview with his imperial father, had great fortifications constructed the next year on the German river. The banks of the Rhine were lined with more than fifty castella, of which the most important, situated opposite the standing camp of Mogontiacum (Mainz), grew into a town in course of time; Bonn was connected by a bridge with the right bank of the royal stream, the high angle between the Rhine, the Main, and the Lahn was guarded by a series of lines on the Taunus which still proclaim their first framer in their name of “Drususgraben.” They formed the basis of that great frontier rampart which in later days divided Roman territory from free Germania.