No, nothing you couldnt witness can be a fact. One could argue the discovery of Americas, existence of Alexander the Great, even Napoleon. And there would be no single thing you could do to scientifically prove they were indeed real. There are just some "sources" you think that are reliable, or that appease you and you would rather "trust" their claims. Should I have lived as a historian in Roman times, I could just persuade other historians and write about how a bear horde ravaged through Rome, and give made up reports on a daily basis, just for ****s and giggles. And now the whole world would think that was an actual event.