In the later Roman Empire, the classical Latin word for horse, "equus", was replaced in common parlance by the vulgar Latin "caballus", sometimes thought to derive from Gaulish "caballos". From "caballus" arose terms in the various Romance languages cognate with the (French-derived) English "cavalier": Italian "cavaliere", Spanish "caballero", French "chevalier" (whence "chivalry"), Portuguese "cavaleiro", and Romanian "cavaler". The Germanic languages have terms cognate with the English "rider": German "Ritter", and Dutch and Scandinavian "ridder". These words are derived from Germanic "rīdan", "to ride", in turn derived from the Proto-Indo-European root "reidh-".