While going through a batch of old silver coins from an auction I came across this 1 Franc - Napoleon III from 1866.

My first impression was that yet another dude with too much time on their hands defaced a coin with some random name.
But upon googling it I discovered it was a piece of history. Translated from cgb.fr:
SATIRICAL COINS - THE WAR OF 1870 AND THE BATTLE OF SEDAN
During the war of 1870, the Army of Châlons, commanded by MacMahon, was joined by Napoleon III on 15 August and attempted to come to the aid of Bazaine, who was trapped in Metz with the Army of the Rhine. On 21 August, the Army of Châlons set out to join MacMahon, but he was surrounded. Defeated several times, notably at Beaumont, the army was repelled and then surrounded at Sedan by the Prussian commander-in-chief Moltke, despite the efforts of Commander Lambert who, wounded, fought with his marines until the last cartridge. On 2 September 1870, crushed by German artillery fire, Napoleon III and 83,000 soldiers of the French army surrendered to the King of Prussia. On 3 September, Napoleon III and William I met, while Paris learned of the emperor's defeat and captivity. Demonstrations broke out with cries of ‘abdication! abdication!’. On 4 September, Napoleon III was deposed and a government of national defence was established.
This caused the fall of the Bonaparte dynasty and the end of Second French Empire.
To “commemorate” this defeat a lot of coins were countermarked with text like the one above or with adaptations to the head of Napoleon III, for instance wearing a German helmet.
Always nice to learn something new 🙂