We can prove the Earth is round ourselves right now. We can't magically know what happened in history if it wasn't accurately recorded or has been lied about for decades.

Edit: To add, we know plenty of things. But we don't know anything about history outside of what they tell us, what was recorded and found, or what we were present for. Number 2 is easy to control if clowns are the only ones uncovering history. They just bury what they don't like.

We can prove the Earth is round ourselves right now. We can't magically know what happened in history if it wasn't accurately recorded or has been lied about for decades.