Cai, 45, who produced a similar spectacular in Vienna in 1999, wants to lay a trail of gunpowder starting under Blackfriars Bridge, moving along the surface of the Thames, across the Millennium footbridge and up to Tate Modern. The instant the trail reaches the top of the Tate's tower, computercontrolled rockets launched from the roof of the museum will explode to form a dragon's tail image in the air. The whole display will last just one minute.