Manipur, the state where the dam is supposed to be built, lies in India's impoverished and insurgency-racked northeast, and is home to tribal groups who have their own distinct culture. Now that culture has brought a major project to build a 520ft hydroelectric dam to a standstill.

Manipur's tribal people say the dam will destroy the lake where the sword of one of their greatest heroes, Jadonang, is believed to lie. It will also submerge an island called Thiledam, meaning 'Life and Death', where they believe the souls of the dead rest, an echo of the isle of Avalon, the supposed resting place of King Arthur.

The Tipaimukh dam will also flood 60 villages and displace 40,000 people. But local beliefs have galvanised opposition far beyond those directly affected, and tribal groups had called for a 24-hour strike and blocked roads across the state.

Government officials say the project to dam the Barak river would guarantee electricity for the state and bring in a billion rupees ( 8bn) a year from power sales. In a state where mass unemployment has fuelled several insurgencies, it could create 4,000 jobs.

But the troubles facing Manipur are not so easy to solve. Like most of the seven states in north-east India, the so-called 'Seven Sisters', it is facing insurgencies by indigenous peoples who feel they have little or no stake in India, and that their affairs are dominated by far-off Delhi. At least 20,000 people have died in the violence since the 1960s.

Against this backdrop, forcing 40,000 indigenous people from their homes and flooding an area of cultural significance was always going to be difficult.