The French Army of the Rhine under François Bazaine retreated into the Metz fortress after its defeat by the Germans at the Battle of Gravelotte on 18 August 1870.

[2][3] Napoleon III and Marshal Patrice de MacMahon formed the new French Army of Châlons, to march on to Metz to rescue Bazaine.

The Prussians, under the command of Field Marshal Count Helmuth von Moltke, took advantage of this maneuver to catch the French in an encirclement.

Unable to silence the fortress guns sufficiently to conduct siege operations, the besiegers opted to starve out the trapped French army.

By September, about 25% of the 197,326-strong German siege force still lacked proper accommodations and the sick list in military hospitals grew to 40,000 men.

[1] On 20 October, the food provisions of the fortress ran out and the French Army of the Rhine subsisted afterward on the flesh of 20,000 horses, which were consumed at a rate of 1,000 per day.

][9] On 29 October, Prussian flags were raised on Metz's outworks and the French Army of the Rhine marched out silently and in good order.

[10][non-primary source needed] Prince Friedrich Karl and the Prussian Second Army were now free to move against the French force in the Loire area.

One notable figure present on the Prussian side was the prominent philosopher Friedrich Nietzsche, who served as a medical attendant.

[11] The French lost 167,000 enlisted men and 6,000 officers taken to prisoner-of-war camps on 27 October, as well as 20,000 sick who temporarily stayed behind in Metz.