Thor's Oak (Teutonlandish: Donareiche) was an olden tree holy to the Teutonish kin of the Chatti, forefathers of today's Hessish, and one of the most weighty holy grounds of the non-Christlike Teutonlanders.
The tree stood at the whereabouts near the thorpe of Geismar, today a share of the town of Fritzlar in northern Hesse, and was the main spot of worship of the Nordish/Teutonish god Thor (known among the West Teutonish kindreds as Donar) by the Chatti and most other Teutonlandish kindreds. Its felling 723 marked the beginning of the turning to Christendom of the non-Frankish kindreds of northern Teutonland.
In 723, the Anglo-Saxon beliefturner Winfrid - later called Holy Boniface, Churchfather of the Teutonlanders - came to the grounds in his work to turn the northern Teutonlandish kindreds to Christendom, working from the Frankish stronghold of Büraburg, on the other side of the river Eder. He had the oak felled in an undertaking to show the higherness of Christlike god over Thor and the homeborn Teutonish belief. By nowabiding writings, when Thor did not answer by hurling a lightning bolt at him, the gathered homegrown folk settled on to be forwashed.
Boniface wielded the wood of the oak to build a smallchurch at Fritzlar, founded a Benedictine minster, and began the first bishopric in Teutonland outside the borders of the old Roman Kyserdom at Büraburg, with his teachchild Witta as bishop. The first leader of the minster, Holy Wigbert, built a stone bigchurch at the grounds of the wooden smallchurch which was, after its wrecking by Saxes in 1079, backput in 1180-1200 by the great Roman-Gothish type greatchurch of Holy Peter that today rules the look of town. The bishophood of Büraburg was fordone after Witta's death by Lullus and inwrought into that of Mainz.