Irminsul

Irminsul, or the Great Pillar, is a pillar-like object carved out of the wood of Yggdrasil which served as the seat of power for Saxnot, patron deity of the Saxons, and therefore was sacred to the Saxons. Because Saxnot's power is connected to Irminsul, destroying it is one of the ways to defeat the God.

The original Irminsul existed in Saxony but was destroyed by Charlemagne in 775 AD, the destruction of Irminsul severely weakened Saxnot and by extension the Saxon people. Many Saxons lost access to their magic and those for those who retained it, their magic was weaker. This is what enabled Charlemagne's later victories and his suppression of Germanic paganism.

The Saxon wars ended in 804, at that point most of the Saxons had lost the will or ability to fight so they converted to Christianity, assimilated, and essentially ceased being Saxons (at least as far as Saxnot was concerned). The rest went underground (similar to the Tweltth Legion Fulminata after the fall of Rome).

At the end of the Saxon Wars their god was left in a state of hibernation. Recently however the Saxons managed to recreate Irminssul and revive their god.