Forum Romanum
Outlines of Roman History: Decline of the Empire: Disintegration of Empire
This article from Morey's 1901 textbook recounts the attacks on the Roman Empire by the Sassinids from the east and the Germanic barbarians from the north.
World History Encyclopedia
World History Encyclopedia: Alemanni
Encyclopedia entry on Alemanni, a confederacy of Germanic-speaking peoples who occupied modern day Germany. Site has maps, links to further material and timeline of events.