The Suebi (Germanic tribe), a Grove where the Race Arose and their god Dwells, and Withing Like a Snake?

They describe the Semnones as the most ancient and best-born tribe of the Suebi: this credibility of their antiquity is confirmed by religion: at fixed seasons all tribes of the same name and blood gather through their delegations at a certain forest—

“Haunted by visions beheld by their sires and the awe of the ages”

—and after publicly offering up a human life, they celebrate the grim “initiation” of their barbarous worship. There is a further tribute which they pay to the grove: no one enters it until he has been bound with a cord: he puts off equality and advertises in his person the might of the deity: if he chance to fall, he must not be lifted up or rise—he must writhe along the ground until he is out again: the whole superstition cames to this, that it was here where the race arose, here where dwells the god who is lord of all things; everything else is subject
to him and vassal. The prosperity of the Semnones enforces the idea: they occupy one hundred cantons, and from their large number it results that they consider themselves the head of the Suebi. 

Tacitus, Cornelius,  Germania, 39.

(Agricola, trans. M. Hutton, rev. by R. M. Ogilvie, Germania, trans. by M. Hutton, rev. by E. H. Warmington, Dialogus, trans. by W. Peterson, rev. by M. Winterbottom, London: W. Heinemann; Cambridge, Mass.: Harvard University Press, 1980, p. 194, 195).