Agios Achilleios (Greek: Άγιος Αχίλλειος, before 1926: Αχίλλειον – Achilleion)[2] is a village in the Florina Regional Unit in West Macedonia, Greece.

In 1014, Tsar Samuel suffered a fatal heart attack after hearing about the Bulgarian loss in the Battle of Kleidion and was buried beneath the basilica.

In February 1948, in the midst of the Greek Civil War, Nikos Zachariadis, the General Secretary of the Communist Party of Greece, married Roula Koukoulou, his long-time lover, on this island, in a widely publicized ceremony.

It remained a sensitive border zone for most of the Cold War, sparsely inhabited and inaccessible to non-residents without a special permit.

Until 2000, when a floating bridge was built, children would travel to school on the mainland by boat in summer and walk across the frozen lake in winter.