'The men ignored him. They were dressed very oddly in dark grey woollen tunics and knee-length leather breeches. And they were wearing open-toed, calf-length leather sandals.... Roman soldier caligae. Lucius shook his head and rubbed his eyes. Panic clawed at his throat with bone-cold fingers; a creeping realisation traced an icy line up his spine.' Toilets. Everybody needs them. Two thousand years ago, on Hadrian's Wall at Housesteads...