reading more about Julius Ceasars battles, I can’t help notice how they refer to the racial groups that he fought. They were either Belgic, Germanic, Celtic, Persians, Britons and so on. He clearly fought distinct racial groups that were largely separate from each other. These races didn’t exactly wear military uniforms to identify each other either.
In close combat battle when thousands of people are swinging swords at each other, you want to make sure that your sword goes into the face of your enemy. You don’t want to kill your buddy. You need to make quick decisions on who lives and who dies in those situations. What is the easiest way to tell who is allied with you? You use visual cues.
Since uniforms, in Roman times, were crudely hand-sewn, not everybody could make the same exact uniform. Peoples clothing looked different, that is assuming if they wore clothes at all. There needed to be other ways to tell who is on your side in battle. The racial traits and recognizable faces would have been the best way to tell who’s friendly and who’s not.
Psychologically, people like what is similar to them. If someone else looks like your brother, you are more likely to have an affinity towards them. It doesn’t mean that you will hate other races on principle, but you tend to share more time with other people who look more similar to you because they may remind you of your family.
Also, the climates and environments had some influence on racial traits. The Scottish highlands are mountainous and cloudy. So you have strong legged white people bounding around the area. Whereas in Italy, it’s more sunny and flat ground. So Italians developed darker skin and bones that could handle long flat ground walks. It takes many generations for these traits to develop.
Of course there was a lot of interbreeding. But that interbreeding probably didn’t span over very long distances, especially in Roman times. Sometimes even the closest of family members breed, which can be risky. It’s not exactly necessary to keep a perfect bloodline going. That practice seemed to have been reserved more for royalty than the common masses.