Mametz

'"For years afterwards the farmers found them - the wasted young, turning up under their plough blades." So run the blunt, grimly beautiful opening lines of the Welsh poet Owen Sheers's elegy for the men, 4,000 of them from the 38th (Welsh) Division, who were killed or wounded in the Battle of Mametz Wood in July 1916. Sheers revisits that chapter of carnage in a stirring, sprawling promenade show...