One of the biggest battles of the three-year Greek Civil War took place in the Grammos mountains in 1948. The operation took place after the Hellenic Army had secured the Peloponnese, where it managed to defeat the DSE's III Division, numbering 20,000 fighters. In the battle of Grammos, forces of the Hellenic Army, with the codename Operation Koronis, deployed 70,000 troops, while the DSE had 12,000 fighters. The battle lasted from 16 June until 21 August 1948. On that day, DSE forces, after hard fight, retreated into Albanian territory and reformed towards Vitsi. The maneuver from Grammos to Vitsi is considered one of the most important tactical actions of DSE during the war, from a military point of view.