 It began with a Frankish invasion of Saxon territory and the subjugation of the Engrians and destruction of their sacred symbol Irminsul near Paderborn in 772 or 773 at Eresburg.Irminsul may have been a hollow tree trunk, presumably representing the pillar supporting the skies—similar to the Nordic tree Yggdrasil and apparently a common belief among the Germanic peoples.Charlemagne's campaign led all the way to the Weser River and destroyed several major Saxon strongholds.