Later that summer, the Russians under Field Marshal Stepan Fyodorovich Apraksin besieged Memel with 75,000 troops. Memel had one of the strongest fortresses in Prussia. However, after five days of artillery bombardment the Russian army was able to storm it. The Russians then used Memel as a base to invade East Prussia and defeated a smaller Prussian force in the fiercely contested Battle of Gross-Jägersdorf on 30 August 1757. In the words of the American historian Daniel Marston, Gross-Jägersdorf left the Prussians with "a newfound respect for the fighting capabilities of the Russians that was reinforced in the later battles of Zorndorf and Kunersdorf". However, the Russians were not yet able to take Königsberg after using up their supplies of cannonballs at Memel and Gross-Jägersdorf and retreated soon afterwards.