One of the oldest man-made structures in the Americas. This shelf of cliff dwellings, built by the pre-Columbian Sinagua people, at Montezuma Castle National Monument dates from the early 1100s. The main “castle” structure is five stories tall and has more than twenty rooms. Perched on the limestone cliffs, the structure is made of limestone set in mortar, similar to modern stone building construction. Additional rooms existed in the cliff, all of which were well away from seasonal flooding.