Megalithic seems more fitting than cyclopean to me.
Interestingly, this dictionary lists three meanings of the word: https://www.thefreedictionary.com/cyclopean
The first is “referring to a Cyclops”. The second is “huge”. The third is in reference to these types of (megalithic) ruins.
I wonder if the first meaning is the original one, and the others evolved from that meaning as our understanding of human history changed.