Siege of Thessalonica (617)

Siege of Thessalonica
Part of the Avar–Byzantine Wars
Map of the northern Balkans in Late Antiquity
Date 617 or 618 Location Thessalonica Result Successful defence of Thessalonica
Belligerents
Byzantine Empire	Avars Sclaveni

The Siege of Thessalonica in 617 or 618 was an unsuccessful siege of the city of Thessalonica, the major Byzantine stronghold in the region, by the Avars and the Slavic tribes (Sclaveni) who had settled in the city's vicinity. The attack was the last and best-organized attempt by the Avars to take the city. It lasted for 33 days and involved the use of siege engines, but in the end failed. The main source for these events are the Miracles of Saint Demetrius, named after Thessalonica's patron saint, Saint Demetrius.

In the last third of the 6th century, the Byzantine Balkans were threatened by large-scale raids of the Avars, based in the Pannonian Plain, and their Slavic allies, based north of the Danube, which marked the border of the Byzantine Empire. The Byzantines, focusing on their eastern border, where they faced the Sassanid Persians in a protracted war, were unable to maintain an effective defence of the region: following the fall of Sirmium in 582 and of Singidunum in the year after, the Balkans lay open to Avar raiding. Along with the Avars, the breach in the Danube limes allowed the Slavic tribes to raid further and further south into Greece, and to begin a gradual process of settlement in these areas, the extent, chronology and other details of which are much debated. During these raids, probably in 586 (although 597 is a possible alternative date), Thessalonica, the most important city in the Balkans except for the imperial capital, Constantinople, was besieged by the Avars and their Slavic auxiliaries for seven days, as described in the Miracles of Saint Demetrius, a collection of miracles attributed to the city's patron saint in two books, one written ca. 610 and the other around 680.

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