Families of soldiers who took part in the lightning Allied advance, which smashed German defences and morale, precipitating the end of the war, have travelled to Amiens from across the world for the ceremony in the city's cathedral.
Representatives of the Australian, British, Canadian, French and US governments will also commemorate the tens of thousands of troops killed in the four days of fighting, along with former German president Joachim Gauck. It marked a shift away from trench to armoured warfare, with the Allies deploying hundreds of tanks to push deep into German lines on what German General Erich Ludendorff called "the black day of the German army" in the war.
May's visit is her second to France in under a week, coming days after she held talks with President Emmanuel Macron at his Mediterranean holiday retreat over her Brexit plan. The British premier, who is under pressure to win allies on the continent for her divorce strategy, will read aloud at the ceremony from the war memoirs of Britain's wartime leader Lloyd George.
Prince William will also address the proceedings, and the two will also meet with soldiers' families, including descendants of the crack Canadian and Australian troops who led the Allies into battle.
Yet despite the Allies landing a decisive blow in Amiens, the battle never gained the same place in the popular imagination as longer, bloodier World War 1 clashes such as the Battles of the Somme or Verdun. By the summer of American troops were pouring into France and the Allies had drastically boosted their firepower, emboldening them to strike back at flagging German forces on the Western Front. Supreme allied commander General Ferdinand Foch convinced the French, British and Americans to mount a stealth attack around the city of Amiens, a key rail and logistics hub.
