BEFORE THE MANOR-HOUSE’S GATES, two equestrians parleyed: a stout, peg-legged Englishman in a coat that had been drab, before it had got so dirty, and a French cavalier. They were ignored by two hundred gaunt, shaggy men with shovels and picks, who were turning the house’s formal garden into a system of earthen fortifications with interlocking fields of fire.