Previously visited on Earth?

Would it be possible for one of the civilizations long time ago to have been visited by some other species of life that we don't know of? Would we have clues or anything or is there no way to know? Have all the glyphs/ancient writing been discovered? Or are there some still unknown and what if somewhere it says something about that? What if one person had known things nobody else knew about because of something like this such as Leonardo Da Vinci? He invented helicopters long ago.