The peoples who conquered the Roman empire had come out of Germania. Although few ancient authors have describe their ways for us, we have two who are of considerable weight. Cæsar, waging war on the Germans, describes  the Germans’ ethos ; and it is on these ways that he calculated some of his enterprises.  A few pages from Cæsar on this matter are volumes.
Tacitus devotes an entire work to the Germans’ ways. It is a short work ; but it is the work of Tacitus, who condensed everything, because he saw everything.
These two authors are so thoroughly in agreement with the law codes which we have of the barbarian peoples, that in reading Cæsar and Tacitus we find these codes everywhere, and in reading these codes we find everywhere Cæsar and Tacitus.
Now if in researching feudal laws I find myself in an obscure labyrinth, full of paths and detours, I believe I am holding the end of the thread, and that I can walk.