The crossing of the Rhine River by a mixed group of barbarians which included Vandals, Alans and Suebi is traditionally considered to have occurred on the last day of the year 406 (December 31, 406). The crossing transgressed one of the Late Roman Empire's most secure limites or boundaries and so it was a climactic moment in the decline of the Empire. It initiated a wave of destruction of Roman cities and the collapse of Roman civic order in northern Gaul. That, in turn, occasioned the rise of three usurpers in succession in the province of Britannia. Therefore, the crossing of the Rhine is a marker date in the Migration Period during which various Germanic tribes moved westward and southward from southern Scandinavia and northern Germania.