The siege of Thessalonica by Slavic forces commenced with a significant three-day assault on the city walls, representing a critical moment in the struggle for control in the Balkans during the late 7th century. Thessalonica, the second-largest city of the Byzantine Empire after Constantinople, was a strategically vital location due to its position on trade routes and its role as a maritime gateway. Slavic tribes had been increasingly encroaching on Byzantine territories, leading to numerous confrontations and territorial disputes. The siege exemplified the growing threat posed by the Slavs to Byzantine authority.

During the three days of coordinated attacks, the Slavic forces employed a range of strategies, including heavy infantry assaults, and siege engines designed to breach the formidable city walls. Byzantine defenders were called to arms, utilizing their knowledge of the terrain and fortifications to withstand the onslaught. The spirit of the defenders was bolstered by their deep-seated attachment to the city, as Thessalonica held both economic and symbolic importance for the Byzantines. The siege wasn't merely a military confrontation; it was a clash of cultures, showcasing the struggle for survival from the Byzantine perspective and the Slavic aspiration for territorial dominance.

Despite the ferocity of the assault, the city walls held firm, and the Slavic forces ultimately withdrew, but not without causing significant alarm in Byzantine circles. The temporary failure of the siege did not diminish the long-term pressures faced by Thessalonica, as the ongoing Slavic expansions would continue to destabilize Byzantine control in the Balkans. This event evidenced the shifting military landscape of the time, paving the way for further interactions and conflicts between Slavs and Byzantines in the ensuing centuries.