Church bells ushered in the morning at villages across a patch of northern France on Saturday, marking the moment 90 years ago that launched one of history's bloodiest episodes, the Battle of the Somme. The poignant tolling began a day of commemorations honoring the soldiers of 20 nationalities who fought in the Somme. But it is Britain that feels the battle's scars most deeply, and Prince Charles and his wife Camilla were to attend ceremonies midday at Thiepval honoring troops who fought in the deadliest day the British army ever saw. The battle has nearly receded from living memory, but its legacy remains. Monuments - from simple markers to major museums - in the fields and towns of the Somme region serve as a reminder of how the Great War changed Europe forever, and how young European unity is. Britain led allied forces into battle July 1, 1916, hoping to end 18 months of deadlock with a decisive Allied victory over German forces. Yet when it ended, after four months of vicious trench warfare ravaging the countryside, Britain had only advanced about six miles (10 kilometers). And more than 1 million troops lay dead.