The Russian forces meanwhile, after the battle of the Alma, had retreated to Sebastopol in order to defend the city, which the allies were preparing to attack. Prince Mentchikof then resolved upon a bold measure for the defence of the city, and this was to sink his ships at the mouth of the harbor, by which he prevented the English and French fleets from entering it, and gained an additional force of eighteen thousand seamen to his army. Loath was the Russian admiral to make this sacrifice, and he expostulated with the general-in-chief, but was obliged to obey. This sinking of their fleet by the Russians reminds one of the conflagration of Moscow,--both desperate and sacrificial acts. The French and English forces were now on the south side of Sebastopol, in communication with their fleet at Balaklava, and were flushed with victory, while the forces opposed to them were probably inferior in number. Why did not the allies at once begin the assault of the city? It was thought to be prudent to wait for the arrival of their siege guns. While these heavy guns were being brought from the ships, Todleben--the ablest engineer then living--was strengthening the defences on the south side. Every day's delay added to the difficulties of attack. Three weeks of precious time were thus lost, and when on the 17th of October the allies began the bombardment of Sebastopol, which was to precede the attack, their artillery was overpowered by that of the defenders. The fleets in vain thundered against the solid sea-front of the fortress. After a terrible bombardment of eight days the defences of the city were unbroken.