Cliff dwellings in Mesa Verde National Park in Colorado, USA

© Brad McGinley Photography/Getty Image

A 50-year balancing act. 50 years of World Heritage Sites

Fifty years ago today, Unesco adopted an international treaty that for the first time linked the concepts of nature conservation and preservation of cultural properties. The World Heritage Sites programme was sparked by Egypt's planned construction of the Aswan High Dam, which would have flooded a large swathe of the Nile Valley and thousands of archaeological treasures.

Mesa Verde National Park in the US state of Colorado, where Ancestral Puebloans lived for seven centuries between 550 and 1300 CE, was among the first World Heritage Sites chosen by the Unesco committee, in 1978. The park was established in 1906 to preserve its incredible heritage. It is home to more than 5,000 archaeological sites, including about 600 cliff dwellings like the one pictured here.