Ancient Roman armor didn't just grow out of the ground, Romans had to invent it first. For a Roman to invent it you first needed some Romans.
The Roman kingdom started with the founding of Rome around 750 B.C. Most likely the city was slowly built up over the years from herders and farmers congregating to Palatine hill. Of course that story isn't very interesting so the Romans have a much more enjoyable creation myth.
Like most stories about ancient times Rome's origin story involves a powerful man and he catches wind about the end of his reign at the hands of a small child. So of course the man, Amulius, like any good villain orders the child or rather children, Romulus and Remus, to be killed. The slave who was ordered to kill the children did what most ordered killers do and put the babies by the side of the river to give them a small chance of survival. Luckily a she-wolf happened by and suckled the babies long enough for a kindly herder to find and adopt the boys. Eventually the boys grew up and found out about their past. They set out to kill their great-uncle and put their grandfather back on the throne of Alba. They succeeded and after much celebration they set out to found their own city. The two brothers couldn't agree on where to build the city, so they each started their city on a different hill. One day when Remus was visiting his dear brother and kindly saying how much better his city was, he jumped over Romulus's wall just to show how it needed a little work. Romulus didn't take criticism well and popped his brother one, outright killing him. Needless to say Romulus's city became the hot place to be.
The ancient Romans were one of the most powerful empires in their time period. They had their military campaigns and strategies down to a science. They built roads all across Europe and parts of Africa and Asia. They developed numbers of architectural marvels including; arches, vaults, massive baths, temples and a Colosseum that showcased Roman gladiator armor. They enjoyed many luxuries like exotic foods and hot and cold water and indoor plumbing. Its no wonder the times period after the fall of the Roman empire is called the dark ages. I could go on and on about Roman achievements but I digress, what allowed so much cultural wealth to blossom in Rome? The Roman military of course, and at it's core was ancient Roman armor.
Roman armor is primarily broken into three separate categories. These three armor types were: Lorica hamata, Lorica squamata, and Lorica segmentata. These most likely aren't the names they were called in Roman times but their true names have been lost somewhere in the mists of time. None of the armor types were used exclusively and they all went through periods where they were more popular or less popular depending on the conditions.