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In page Switzerland:

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Around 260 AD, the fall of the Agri Decumates territory north of the Rhine transformed today's Switzerland into a frontier land of the Empire. Repeated raids by the Alamanni tribes provoked the ruin of the Roman towns and economy, forcing the population to shelter near Roman fortresses, like the Castrum Rauracense near Augusta Raurica. The Empire built another line of defence at the north border (the so-called Donau-Iller-Rhine-Limes). At the end of the fourth century, the increased Germanic pressure forced the Romans to abandon the linear defence concept. The Swiss Plateau was finally open to Germanic tribes.[citation needed]