The Romans were known for taking technology and advancements from other peoples they encountered and making them their own. This pattern holds true in military affairs; indeed, little of the Roman military was indigenously developed. This dissertation looks at the origins of the Roman's mainline weapons systems from the beginning of Roman Republic expansion in the fourth century BC to the abandonment of Western-style armaments in favor of Eastern style ones beginning in the late-third century AD. This dissertation determines that the Romans during that time relied predominately on the Celtic peoples of Europe for the majority of their military equipment. One arrives at this conclusion by examining at the origins of the major weapons groups: armor, shields, spears, swords, and missile weapons. This determination is based on the use of ancient written sources, artistic sources, and archaeological sources. It also uses the large body of modern scholarship on the individual weapons. The goal is to produce a unified work that addresses the origins of all weapons in order to see if there is an overarching impact on the Roman military from outside cultures. When one studies whence the weapons that ended up in Romans hands originated, a decided Celtic …