Helots - The slave class of Sparta
Something to keep in mind and that you realize after a while is that the history you know without much research or certainty is most likely the history of the ruling class, told to make they look as great as they believe to be.
I have just read Three by Kieron Gillen, the intentional Spiritual Antithesis to 300 by Frank Miller. I knew 300 is propaganda that only values the importance of a small portion of the people who fought. Spartans were the real soldiers, the superior people, the only that mattered. Then you have a class of people whose job is to do whatever they don't deem dignified, and fight their battles as well if needed. A class they rightfully feared for outnumbering their oppressors and revolting whenever the opportunity arose. A class they openly mistreated.
It's been two decades since I left school, but I'm pretty sure there was no mention of them in my history lessons. I recall the wars, but omitting the detail that most of the soldiers (in the practical sense) were not who you'd assume to be is huge.