The Łódź Insurrection was an uprising by Polish workers in Łódź against the Russian Empire which took place between 21 and 25 June 1905. The Russian-controlled Congress Poland was one of the major centers of the Russian Revolution of 1905, and the Łódź Insurrection was a key incident in those events. For months prior to the uprising, workers in Łódź had been in a state of unrest, with several major strikes brutally quelled by the Russian police and military. Around 21–22 June, angry workers began building barricades and assaulting police and military patrols. The riots began spontaneously, without backing from any organized group; Polish revolutionary groups were taken by surprise and did not play a major role in the subsequent events. Authorities declared martial law and called in additional troops. No businesses operated in the city on 23 June as the police and military stormed dozens of workers' barricades. Eventually, by 25 June, the uprising was crushed, with estimates of several hundred dead and wounded. The events were reported in international press and recognized by socialist and communist activists worldwide.