In the course of these processes, by the beginning of the October Revolution, the Bolsheviks were gaining a majority, primarily in the Soviets of Workers' and Soldiers' Deputies of large industrial cities, gaining up to 90% of the seats in the Petrograd Soviet and up to 60% in Moscow. On September 17, 1917, the Bolshevik Viktor Nogin became Chairman of the Presidium of the Moscow Soviet; on September 25, the Petrograd Soviet was headed by Leon Trotsky. Relying on their firm majority in the Petrograd Soviet, the Bolsheviks were able, despite the opposition of the All-Russian Central Executive Committee, to convene the Second All-Russian Congress of Soviets of Workers' and Soldiers' Deputies and prepare for the October Armed Uprising.