Of the military-political organisation of Germany, as at that time planned, we have but a very imperfect knowledge, because, on the one hand, there is an utter want of accurate information as to the arrangements made in earlier times to protect the Gallic eastern frontier, and, on the other hand, those made by the two brothers were in great part destroyed by the subsequent development of affairs. There was no attempt to move the Roman frontier-guard away from the Rhine; to this matters might perhaps come, but they had not yet done so. Just as was the case in Illyricum at that time with the Danube, the Elbe was doubtless the political boundary of the empire, but the Rhine was the line of frontier-defence, and from the camps on the Rhine the connections in rear ran to the great towns of Gaul and to its ports.[10] The great headquarters during these campaigns was what was afterwards named the "Old Camp," Castra vetera, (Birten near Xanten), the first considerable height below Bonn on the left bank of the Rhine, from a military point of view corresponding nearly to the modern Wesel on the right. This place, occupied perhaps since the beginning of the Roman rule on the Rhine, had been instituted by Augustus as a stronghold for curbing Germany; and, if the fortress was at all times the basis for the Roman defensive on the left bank of the Rhine, it was not less well chosen for the invasion of the right, situated, as it was, opposite to the mouth of the Lippe which was navigable far up, and connected with the right bank by a strong bridge. The counterpart to this "Old Camp," at the mouth of the Lippe was probably formed by that at the mouth of the Main, Mogontiacum, the modern Mentz, to all appearance a creation of Drusus; at least the already mentioned cessions of territory imposed on the Chatti, as well as the constructions in the Taunus to be mentioned further on, show that Drusus clearly perceived the military importance of the line of the Main, and thus also that of its key on the left bank of the Rhine. If the legionary camp on the Aar was, as it would seem, instituted to keep the Raeti and Vindelici to their obedience (p. 18), it may be presumed to have been laid out about this time; but then it had merely an outward connection with the Gallico-German military arrangements. The legionary camp at Strassburg hardly reaches back to so early a time. The line from Mentz to Wesel formed the basis of the Roman military dispositions. That Drusus and Tiberius had--apart from the Narbonese province which was then no longer imperial--the governorship of all Gaul as well as the command of all the Rhenish legions, is an ascertained point; apart from these princes, the civil administration of Gaul may at that time perhaps have been separated from the command of the troops on the Rhine, but scarcely was the latter thus early divided into two co-ordinate commands.[11] [Sidenote: Positions on the right bank of the Rhine.]