Examples of social injustice?

I need some examples of social injustice from history for a story that i plan to write.

I will be writing from the point of view of a relatively ordinary person's perspective, and how they will be effected.

The more ancient, the better, as i am a great fan of writing historical fiction.

I'm not asking for any plot, just an era or event that i can sink my teeth into. As long as there is some sort of injustice that was either sanctioned or encouraged by the powers of that time. (Or where they turned a blind eye).

Thanks loads.