On the sixth day of Ukraine’s advance into Kursk Oblast in southern Russia, there’s growing evidence the Ukrainian invasion corps—some or all of up to five 2,000-person brigades plus at least one 400-person independent battalion—plans to stay.

The Ukrainians are digging trenches. Anticipating static warfare along or near the existing front line, the Russians are digging in, too.

That both sides are fortifying their positions doesn’t mean the Ukrainians are done advancing. Nor does it mean the Russians can’t counterattack—and push the Ukrainians back to the border, 10 miles away.

But it does mean that stabilization of the front line—and a long-term Ukrainian occupation of part of Kursk—is on the table.