The ‘Fortress Belt’: Ukraine’s Last Line of Defense

If a string of fortified cities in northwestern Donetsk is breached, Russia will likely achieve its longstanding goal of capturing the entire Donbas region.

Ukrainian soldiers fire a mortar at Russian positions near Kostyantynivka on Aug. 26, 2025. Iryna Rybakova/Ukraine's 93rd Mechanized Brigade via AP

Ukraine hopes a string of fortified cities in northwestern Donetsk—dubbed the “fortress belt”—will be able to stop any further Russian advance.

That belt is also exactly an area that Russia might demand as part of a peace deal.