Square Tower House in Mesa Verde National Park, Colorado

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Castle of the Ancestral Puebloans. Square Tower House in Mesa Verde National Park

We continue our celebration of National Park Week (through April 24)–and the UNESCO International Day for Monuments and Sites–with a visit to the impressive Square Tower House in Mesa Verde National Park. Square Tower House is one of many cliff dwellings constructed by the Ancestral Puebloans in what is now the American Southwest. At 27 feet, it's the tallest structure in the park. Square Tower House is also notable for its kiva, a round, sunken room used for ceremonies. Unlike most of the ancient kivas found in the region, the kiva at Square Tower House has an intact original clay roof supported by wooden beams.

Ancestral Puebloans lived in today's Four Corners region, where the borders of Colorado, Utah, Arizona, and New Mexico meet at a single point. It's unclear when exactly this culture emerged, but the current consensus is that the Ancestral Puebloans appeared in this area a little more than 3,000 years ago. They're believed to have built the series of cliff dwellings for defensive reasons as various factions competed for scarce resources when the region suffered from a prolonged drought. It's thought that the changing climate eventually became so severe that it likely drove them from the cliff dwellings sometime around 1300 CE, just a century or so after construction began. Today, many of the cliff dwellings have been restored and visitors can view the homes and kivas of the builders.