After the campaigns of Germanicus and the death of Hermann, a long time elapsed during which the relation of Germany to the Roman Empire might be called a truce. No serious attempt was made by the unworthy successors of Augustus to extend their sway beyond the banks of the Rhine and the Danube; and, as Tiberius had predicted, the German tribes were so weakened by their own civil wars that they were unable to cope with such a power as Rome. Even the Cherusci, Hermann's own people, became so diminished in numbers that, before the end of the first century, they ceased to exist as a separate tribe: their fragments were divided and incorporated with their neighbors on either side. Another tribe, the Ampsivarii, was destroyed in a war with the Chauci, and even the power of the fierce Chatti was broken by a great victory of the Hermunduri over them, in a quarrel concerning the possession of a sacred salt-spring. About the middle of the first century, however, an event is mentioned which shows that the Germans were beginning to appreciate and imitate the superior civilization of Rome. The Chauci, dwelling on the shores of the North Sea, built a fleet and sailed along the coast to the mouth of the Rhine, which they entered in the hope of exciting the Batavi and Frisii to rebellion. A few years afterwards the Chatti, probably for the sake of plunder, crossed the Rhine and invaded part of Gaul. Both attempts failed entirely; and the only serious movement of the Germans against Rome, during the century, took place while Vitellius and Vespasian were contending for the possession of the imperial throne. A German prophetess, of the name of Velleda, whose influence seems to have extended over all the tribes, promised them victory: they united, organized their forces, crossed the Rhine, and even laid siege to Mayence, the principal Roman city. [Sidenote: 70. THE INVASION OF CEREALIS.] The success of Vespasian over his rival left him free to meet this new danger. But in the meantime the Batavi, under their chief, Claudius Civilis, who had been previously fighting on the new Emperor's side, joined the Gauls in a general insurrection. This was so successful that all northern Gaul, from the Atlantic to the Rhine, threw off the Roman yoke. A convention of the chiefs was held at Rheims, in order to found a Gallic kingdom; but instead of adopting measures of defence, they quarrelled about the selection of a ruling family, the future capital of the kingdom, and other matters of small comparative importance.