The day of National Celebration of the Greek Resistance was established by the government in 1982 and observed on 25 November, to commemorate the most important joint operation of Greece’s major resistance groups formed in World War II.
The demolition of the Gorgopotamos Bridge was carried out on 25 November 1942, by the combined forces of the Greek People's Liberation Army (ELAS), the National Republican Greek League (EDES) and British commandos of the Special Operations Executive (SOE). It is regarded as a major act of resistance during the Second World War, and was a significant instance of successful cooperation between Greece’s resistance movements.
Following the German invasion of 1941, which resulted in the Triple Occupation of Greece by Germany, Italy, and Bulgaria until 1944, a number of resistance organisations began emerging in Greece, most of them aligned with the various political and ideological factions of the time.
The largest organisation, with a membership estimated between half and two million, was the National Liberation Front (EAM), which was founded on 27 September 1941 by representatives of four left-wing parties: the Communist Party of Greece (KKE), the Socialist Party of Greece (SKE), the Union of People's Democracy (ELD) and the Agricultural Party of Greece (ΑΚΕ). It was led by Georgios Siantos, acting leader of KKE. Its military wing, the Greek People's Liberation Army (ELAS), under Chief Captain Aris Velouchiotis, quickly grew into the largest armed guerrilla force in the country, and the only one with nation-wide presence.