In 1854, the Siege of Sevastopol begins during the Crimean War, as the French sapeurs begin digging trenches around the capital of the Crimea.
After the Allied fleet — which included the British and Ottomans along with the aforementioned French — landed in September with 50,000 men at Eupatoria, the intention was to march to Sevastopol with ease.
It didn’t quite go as planned. The Russians scuttled the fleet and began firing on the assembling Allies. The battle was won by the Allies nearly a year later, but at great cost: 128,000 casualties for the Allies, 102,000 for the Russians, which included civilians, many of whom died of disease in the encircled city.