Siege of Deir ez-Zor

Battle context

The Siege of Deir ez-Zor represented one of the longest sustained engagements of the Syrian Civil War, with Islamic State forces maintaining a blockade of Syrian government-held districts in the city for nearly three years and two months. IS sought to capture Deir ez-Zor in order to consolidate full control over Deir ez-Zor Governorate, a strategically significant objective given the region's importance to IS territorial ambitions in eastern Syria. Government forces numbering between 4,000 and 5,000 held out against an IS contingent estimated at up to 15,000 fighters. The siege ultimately failed in its objective: the Syrian Army broke through and fully recaptured the city within nine weeks of launching a relief offensive. The duration of the siege and its eventual outcome made Deir ez-Zor a marker of both IS operational reach at its height and the limits of its ability to reduce a defended urban enclave, while the government's eventual recapture signaled a decisive shift in IS's capacity to hold and expand territory in eastern Syria.