A worker on a tractor drives next to a recently prepared trench system on the Kupiansk direction, in the Kharkiv region, on January 29, 2024, amid the Russian invasion of Ukraine. After Kyiv's counter-offensive failed to punch through Russian lines last year, Kyiv has switched to the defensive -- building up its own lines of protection to thwart a possible Russian offensive. No side has made a significant territorial gain in more than a year, but fighting has remained intense. For Ukraine, building trenches marks a radical change in approach. The stronger each side's defensive positions become, the greater the risk is that the front lines stay static and the conflict turns frozen. That would complicate Kyiv's objective of liberating the approximately 20 percent of its territory under Russian control. (Photo by Roman PILIPEY / AFP)