The Battle of Tours and the "Battle of Catalonian Plains" (fought near Troyes, France in 451 AD, in which the Romans/Visigoths turned back Attila the Hun/Ostrogoths) might be considered the battles that saved Europe from Arab/Berber and Turko/Mongol invasion, respectively. It is not clear how much either invader would have gained had they won, given their stretched supply lines. In any case, we can thank the Franks and other Germanic tribes occupying France at the time, for saving our Western/Christian bacon. I believe that neither battlefield has been located exactly, the Tours battlefield most likely being near Moussais-la-Bataille, and the "Catalonian Plains" being near Châlons-en-Champagne. Funny how after roughly 1500 years of dispute between Arab/Turkic Islam and European Christians, the main geographic changes are merely the regain of Spain and the loss of Turkey.