[Bear_in_RoseBear]

My own pet theory (based on nothing, other than an assessment of human intelligence and ability) is that there have probably been several periods of human civilization... some perhaps as advanced as the Middle Ages we are familiar with. As to where they went, I think it likely they were destroyed by various natural calamities, such as plague, climate change, volcanic activity, even asteroid strikes.

We're probably overdue for some such calamity in our own civilization....

[blam]

"I think it likely they were destroyed by various natural calamities, such as plague, climate change, volcanic activity, even asteroid strikes.

"We're probably overdue for some such calamity in our own civilization...."

I agree 100%

Did Asteroids And Comets Turn The Tides Of Civilization?