The Gorlice–Tarnów Offensive started as a minor German offensive to relieve Russian pressure on the Austro-Hungarians to their south on the Eastern Front, but resulted in the total collapse of the Russian lines and their retreat far into Russia. The continued series of actions lasted the majority of the campaigning season for 1915, starting in early May and only ending due to bad weather in October. After a heavy artillery bombardment, German Commander August von Mackensen launched an attack which caught the Russians by surprise. The central Powers shattered the Russian defenses, and the Russian lines collapsed. The Russians were forced to withdraw, the Central Powers recaptured most of Galicia, and the Russian threat to Austria-Hungary was averted.