The history of human habitation in the Andean region of South America stretches from circa 15,000 BCE to the present day. Stretching for 7,000 km (4,300 mi) long, the region encompasses mountainous, tropical and desert environments. This colonisation and habitation of the region has been affected by its unique geography and climate, leading to the development of unique cultural and societal organisation. Study of the history of the Andean region began in the 20th century, involving both historical and archaeological investigation.