My old theory was that the Mayans built the stone structures on Hailfire Peaks, seeing as it and Mayahem Temple are directly connected. Then when the dragon came it caused the volcano to erupt, driving the Mayans away to their new home. It's hard to believe anyone built such structures WHILE there was lava everywhere after all, and there's evidence on the Ice Side as well that it was once lush, and was not always frozen over. I feel like the presence of the dragons is what causes the extreme temperatures in the first place
But I realized today I was way overthinking it. The stone stuff is supposed to be Roman as a reference to Vesuvius/Pompeii. That's why it has a colosseum and "HIIO" instead of H2O in the water pool.
The old design made the Vesuvius thing more obvious, with more stone buildings and a lava aquaduct.....lavaduct.