Link to Wikipedia’s article “Bonar’s Oak.” Above is a depiction of Boniface destroying Thor’s oak from The Little Lives of the Saints (1904), illustrated by Charles Robinson.

I have read that officials in the Roman Empire often described Christianity as a form or atheism, since Christians disbelieved in all gods but one (or all gods but three, as some observers of Christianity counted). In light of that description of Christianity, I found this story from the Middle Ages intriguing:

… encouraged by Pope Gregory II, Boniface traveled throughout the pagan lands of Germany on a new mission. In 723 Gregory II consecrated him a bishop so he could travel freely, ordaining priests and other bishops to establish new dioceses. 

Boniface was soon to be famed for a courageous act he performed at Geismar in Hesse (in western Germany). The local community worshiped a great oak tree, believing it to be the sanctuary of the god Thor. They thought that showing disrespect to the three would cause an angry Thor to punish them, but when Boniface felled the great tree, nothing happened. Those who witnessed this were convinced that Boniface could only be right in preaching that the Christian God was stronger than their own. According to the story, Boniface built a chapel with the wood from the tree …

– Michael Collins and Matthew A Price, The Story of Christianity: A Celebration of 2,000 Years of Faith, p. 86.