The extraordinary indifference of the historians Paterculus and Suetonius to chronology, and their absolutely casual use of such connectives as “hereupon,” “soon afterwards,” and the like, makes it difficult to be certain of the real sequence of events. It is, however, certain that Tiberius was Governor of Transalpine Gaul for a year at some period between B.C. 20 and B.C. 16, that he was harassed during the term of his Governorship by sporadic invasions of German tribes, and was able to measure their importance as affecting the peace of his Province, and form plans for permanently checking them. He came to the conclusion that the whole middle and eastern Alpine region was a centre of disturbance, and that it could not be dealt with alone, seeing that the tribes who lived on the Dalmatian coast and at the sources of the Save were always ready to create a diversion when the Roman armies were occupied in the valleys to the south or north-west of the Alps. Cæsar had more than once been called back from the conquest of Gaul to deal with the Pirustæ in the same quarter. In B.C. 16 the ill-omened Marcus Lollius sustained a serious defeat at the hands of the German tribes, while Gaul itself had been rendered unquiet by the exactions of Licinus, himself a Gaul employed by Augustus as Governor in the Southern Province. Augustus himself went to Gaul to set straight the civilian administration, Agrippa was sent to the Illyrian regions, Drusus to the passes leading from Lombardy to the Upper Rhine, while Tiberius took charge of an expedition directed upon the same region from Basle by the Lake of Constance. This was the first of the great combined movements originated by Tiberius; their conception, but even more their success, mark him out as a general of genius. Given a mobile enemy able to live on the country, and provided with an interminable area at his rear into which he can retreat, the only hope of dealing with him successfully is to cut off his retreat. This was the strategy of Tiberius.