9. Casa Grande Ruins (Arizona)
Casa Grande Ruins, located in Arizona, is one of the oldest and most mysterious prehistoric structures in North America. Built by the Hohokam people around 1350 CE, the site features a massive four-story earthen building, thought to have served as a ceremonial or astronomical center.
Made from caliche (a type of natural concrete), the “Great House” demonstrates advanced engineering skills in a desert environment. The Hohokam also created extensive irrigation canals to support agriculture. The exact purpose of Casa Grande remains uncertain, adding to its intrigue. Today, it stands as a protected national monument and a testament to ancient ingenuity and resilience.
