The valley of Yaghnob river in Central Tajikistan owns its fame mainly to the language spoken by the people inhabiting the central sector of the valley. Yaghnobi language is, in fact, the only living remnant of a variety of Sogdian language. Since the late XIX century, Yaghnobis and their language became to be considered as living fossil of a – mythologised – disappeared past. Scholars, and Yaghnobis themselves, often explained the conservation of the original Eastern Iranian variety as a result of the isolation of Yaghnobi people, cut off from the outside world by impassable mountains. In this paper a different view is outlined. Considering the reports of scholars and explorers who visited Yaghnob between late XIX and early XX century and the data collected during several field-works in Yaghnob and surrounding areas (2007-2012), the author tries to demonstrate that Yaghnobi isolation is a matter more of socio-economic marginality than geographic seclusion. To corroborate this thesis some famous case studies in the field of mountain anthropology are considered in a comparative perspective. Moreover, a brief analysis of Yaghnobi lexicon (in particular kinship terms and numerals) has been carried on to demonstrated how Yaghnobi language has been permeated by the contact with outer groups.