User blog comment:Gemini12/How long has the world had the 3 great powers/@comment-3060121-20120624025752

I'm guessing that Yonkou level pirates existed, not sure if there were four tops ones or not. As far as Shichibukai maybe. Brook refered to Moria as a Shichibukai even though he was on the sea for years. He explained who Moria was in his flash back but not his title. But this could be because the Straw Hats already showed that they knew what a Shichibukai was. Brook probably heard it while on Thriller Bark his 1st time