In mid-1758 Prussia invaded Moravia, besieging Olmütz in late May. The city was well defended, and by late June the Prussians' supplies were exhausted. Austrians intercepted and destroyed a major Prussian supply convoy on 30 June in the Battle of Domstadtl, and the invaders abandoned the siege, retreating into Upper Silesia. Russian forces advanced through East Prussia to threaten Brandenburg, fighting the Prussians to a costly draw on 25 August at the Battle of Zorndorf. An Austrian army advancing into Saxony made little progress, despite winning a substantial victory at the Battle of Hochkirch on 14 October.