Once a vast expanse of water and reedbed covered much of Cambridgeshire, Lincolnshire and Norfolk. In the 1650s the ‘Gentleman Adventurers’ hired Dutch engineer Sir Cornelius Vermuyden to drain what they saw as unproductive quagmire and convert it into farmland. Despite the resentment of the local Fen people, who held a deep fondness for their way of life in this bewitching land, the drainage process began. To empty the marshes was an enormous undertaking, so huge drains, pumps and sluice systems were designed to do the job.

Mysteriously, new dams broke, bridges set alight and Vermuyden’s ‘Duchies’ sometimes disappeared without trace. A band of local guerrilla activists, the Fen Tigers, were blamed for taking direct action desperate to save the land they loved. Yet slowly but surely the land was transformed beyond recognition. Meandering river channels were straightened, and new ones dug while levee banks were built up. However, as the earth dried it shrunk, leaving rivers higher than the land around them. So the Denver Sluice complex evolved, an extrordinary feat of civil engineering sitting at the confluence of five watercourses. This structure controls water levels over thousands of acres of land. And it’s been doing so for more than 400 years, listed on the ‘European Route of Industrial Heritage’. But engineering water is complicated. The first sluice failed in 1713, rebuilt by Labelye. And in 1953 a deadly storm surge broke through, flooding 380 square miles of Fenland. Perhaps the Fen Tigers will have their day yet.