On the Eastern front, the war started out equally poorly. The Austro-Hungarian Army was defeated at the Battle of Lemberg and the great fortress city of Przemyśl was besieged and fell in March 1915. The Gorlice–Tarnów Offensive started as a minor German offensive to relieve the pressure of the Russian numerical superiority on the Austro-Hungarians, but the cooperation of the Central Powers resulted in huge Russian losses and the total collapse of the Russian lines and their long retreat into Russia. The Russian Third Army perished. In summer 1915, the Austro-Hungarian Army, under a unified command with the Germans, participated in the successful Gorlice–Tarnów Offensive. From June 1916, the Russians focused their attacks on the Austro-Hungarian army in the Brusilov Offensive, recognizing the numerical inferiority of the Austro-Hungarian army. By the end of September 1916, Austria–Hungary mobilized and concentrated new divisions, and the successful Russian advance was halted and slowly repelled; but the Austrian armies took heavy losses (about 1 million men) and never recovered. The Battle of Zborov (1917) was the first significant action of the Czechoslovak Legions, who fought for the independence of Czechoslovakia against the Austro-Hungarian army. However the huge losses in men and material inflicted on the Russians during the offensive contributed greatly to the revolutions of 1917, and it caused an economic crash in the Russian Empire.