Believing the northern approaches to the city too well defended, especially because of the presence of a large star fort and the city being on the south side of the inlet from the sea that made the harbour, Sir John Burgoyne, the engineer advisor, recommended for the allies attack to Sevastopol from the south. The joint commanders, Raglan and St Arnaud, agreed. On 25 September, the whole army began to march southeast and encircled the city from the south after it had established port facilities at Balaclava for the British and at Kamiesch for the French. The Russians retreated into the city.

The siege of Sevastopol lasted from October 1854 until September 1855, during the Crimean War. During the siege, the allied navy undertook six bombardments of the capital. The city of Sevastopol was the home of the Tsar's Black Sea Fleet, which threatened the Mediterranean. The Russian field army withdrew before the allies could encircle it. The siege was the culminating struggle for the strategic Russian port in 1854–55 and was the final episode in the Crimean War.