The 1978 Thessaloniki earthquake (Greek: Μεγάλος Σεισμός της Θεσσαλονίκης) occurred on 20 June at 23:03 local time.

The shock registered 6.5 on the moment magnitude scale, had a maximum Mercalli intensity of VIII (Severe), and was felt throughout northern Greece, Yugoslavia and Bulgaria.

[4] It was the first earthquake that hit a big city in Greece in modern times.

It is estimated that 49 people died, 37 of which were living in the same block of flats in the city center that collapsed.

There have also been some recorded damage to various local archaeological monuments, such as the Arch of Galerius and Rotunda and the Church of the Acheiropoietos.