The Battle of Gravelotte, or Gravelotte–St. Privat (18 August), was the largest battle during the Franco-Prussian War. It was fought about 6 miles (9.7 km) west of Metz, where on the previous day, having intercepted the French army's retreat to the west at the Battle of Mars-La-Tour, the Prussians were now closing in to complete the destruction of the French forces. The combined German forces, under Field Marshal Count Helmuth von Moltke, were the Prussian First and Second Armies of the North German Confederation numbering about 210 infantry battalions, 133 cavalry squadrons, and 732 heavy cannons totaling 188,332 officers and men. The French Army of the Rhine, commanded by Marshal François-Achille Bazaine, numbering about 183 infantry battalions, 104 cavalry squadrons, backed by 520 heavy cannons, totaling 112,800 officers and men, dug in along high ground with their southern left flank at the town of Rozerieulles, and their northern right flank at St. Privat.

On which date was the Battle of Gravelotte?