The Susa Valley situated between Maurienne, France and Turin, Italy, has been urbanised by the economic development of the region. Scarred by infrastructure like the Frejus highway, an international railway, and numerous dams, tunnels and industries, this "development" has had significant environmental and social impacts. The high speed train line (Treno Alta Velocità in Italian, or TAV) between Turin and Lyon is planned at the intersection of 2 main European axes to complement the European railway network by increasing the transport of passengers as well as goods. The train would pass through the Susa Valley, via 2 main tunnels and numerous shorter ones to cross the Alps. The "No TAV" movement is the grass-roots movement of the Susa Valley population against the construction of the line. This article, explores the motives and rationale of opponents and proponents, highlighting the role of power relations and an underlying clash of ideologies. It shows how the success and longevity of No TAV movement relies on one hand on the versatility and diversity of its arguments, and on the other, a renewed legitimacy in the context of the current social and economic crises of its arguments in favour of strong sustainability, degrowth and participatory democracy.