had seven legions under his command. In spring of 12 BC, he embarked an expeditionary force, perhaps consisting of the Legiones I Germanica and V Alaudae, by ship from the vicinity of modern Nijmegen, making use of one or more canals he had built for the purpose. Drusus sailed to the mouth of the Ems and penetrated into the territory of the Chauci in present-day Lower Saxony. The Chauci concluded a treaty acknowledging Roman supremacy, and would remain allies of Rome for years to come. As they continued to ascend the Ems, the Romans were attacked by the Bructeri in boats. Drusus' forces defeated the Bructeri, but, as it was now late in the campaign season, turned back for their winter quarters in Gaul, taking advantage of their new alliance with the Frisii to navigate through the difficult conditions on the North Sea. As a reward for the successes of his campaign in 12 BC, Drusus was made praetor urbanus for 11 BC when he returned to Rome for the winter. News of Drusus' achievements—navigating the North Sea, carrying the Roman eagles into new territory, and fixing new peoples into treaty relations with Rome—caused considerable excitement in Rome and were commemorated on coins. In the spring of his term as praetor urbanus, he set out for the German border once more. This time, he assembled a force consisting of all or part of five legions in addition to auxiliaries and, setting out from Vetera on the Rhine, ascended the River Lippe. Here he encountered the Tencteri and Usipetes, whom he defeated in two separate engagements. He reached the Werra Valley before deciding to turn back for the season, as winter was coming on, supplies were dwindling, and the omens were unfavorable. While his forces were making their way back through the territory of the Cherusci, the latter tribe laid an ambush for them at Arbalo. The Cherusci failed to capitalize on their initial advantage, whereupon the Romans broke through their lines, defeated the Germanic attackers, and acclaimed Drusus as imperator. To show his continued mastery of the ground, Drusus garrisoned a number of positions within Germania during the winter of 11–10 BC, including one somewhere in Hesse and one in Cheruscan territory, probably either the camp at Haltern or that at Bergkamen-Oberaden, both in present-day North Rhine–Westphalia. He rejoined his wife Antonia and two children for a time in Lugdunum