It was so attractive that the people of Lille were already flocking to it, months before the official opening: two hectares of green grass, 250 shady chestnut and lime trees, fountains and a children's play area, all bang in the middle of France's biggest and busiest northern city.

　　Sadly, the brand-new Parc Jean-Baptiste Lebas is currently firmly closed, its perimeter fence patrolled by watchful policemen while a mine clearance team more used to working in Bosnia, Afghanistan and Iraq finishes ridding it of a potentially deadly crop of first world war grenades. So far they have found some 200.

　　"Thankfully no one has been hurt, but obviously we have to to take every possible precaution," said a city hall official. "There is no question of anyone else being allowed in again until we are sure it's safe."

　　The scare started this month when the parents of a four-year-old boy found him playing with a lemon-sized lump of hardened earth which, on closer inspection, turned out to be a German Heer Handgranat dating from 1915, containing 30 grams (1oz) of unstable explosive, and capable of maiming anyone within a 25-metre radius.

　　Gardeners and building workers on the site next to the city hall began hunting for more with rakes, at first with little success. But then a park visitor stumbled across another one, and "quite suddenly, a whole bunch came to the surface after some heavy rainfall", the official said. The town hall called in a Toulouse-based demining company.

　　Using advanced metal detectors, the company, Geomines, has spent five days inching across the new park, until recently a five-lane boulevard and car park, uncovering first eight, then 23, then 70, then 96 and finally 189 of the grenades, some twisted by earthmovers that had, miraculously, failed to set them off.

　　ISS Espaces Verts, the contractors, told the local newspaper La Voix du Nord that after a painstaking inquiry it had come to the conclusion that of the tens of thousands of tonnes of soil it had trucked in to create the park, a portion came from the villages of Santes, Loos and Wambrechies - through which, for many months, ran the frontline of the 1914-18 war.

　　"We've been lucky," the city hall official said.

　　The people of Lille are used to such scares: three years ago, more than a thousand were evacuated when workers uncovered a 110kg British bomb buried on the site of the new regional council building.