 Under the emperors, Domitian (81-96), Trajan (98-117) and Hadrian (117-138), the Rhaetian Limes was built as a border facing the Germanic tribes to the north.This defensive line ran through the south of Franconia and described an arc across the region whose northernmost point lay at present-day Gunzenhausen.To protect it, the Romans built several forts like Biriciana at Weißenburg, but by the mid-third century, the border could no longer be maintained and by 250 A.D. the Alemanni occupied the areas up to the Danube.