cultures all around the world talk about a huge flood, the hopi indians have one (also talking about the ant friends coming and bringing them underground to be saved), according to the aztec the world gets destroyed repeatedly with the last time it being destroyed being by a huge flood, the bible of course. just look at this list
https://en.wikipedia.org/wiki/List_of_flood_mythswhen everybody independently says the same I tend to believe them.
according to graham hancock the pyramids align with the orions belt in their positions 12500 years ago which is the same point of time the constillation of draco alignes with angkor wat perfectly (also according to graham hancock) making me think the last great cataclysm which probably was the flood shortly after those 2 were built (or in case of angkor wat they were build not that long ago but on older remains which are probably from that time).
Some other interesting stuff showing ancients knowing a lot they shouldnt according to Mainstream History. (From the fallen angels?)
https://www.youtube.com/watch?v=L777RhL_Fz4 This one is partly about modern monuments and their meanings too, but at around 1:10:00 he starts talking about the pyramids, and how they encode the size of the earth in relation to the moon, as well as the speed of light with over 99% accuaricy.
https://www.youtube.com/watch?v=k7rAIcIwBNQ this video talks about how different monuments, from the pyramids, to stonehenge, to stuff in south america encode mathematical knowledge as well as functioning as a GPS telling people where they are currently if they know how to read the monuments, again showing that those "cavemen" were far more sophisticated than we care to admit as well as showing that there was some kind of global communication going on (not like the internet, but information where exchanged through traveling, trade or whatever despite southamerica not being discovered officially until thousands years later) since they all use the same system