Near one of the deadliest front lines of the war in Ukraine, a vast complex of trenches, traps and other obstacles has sprung up in recent months.
The fortifications were built by Russia to slow Ukraine from trying to take Popasna, a town Russia captured in May. They are just a tiny part of an immense Russian defensive network spreading across Ukraine, a New York Times analysis of satellite radar data shows.
These structures could buy Russia crucial time to mobilize and train additional troops to regain momentum in the war. But Ukraine may test Russia's ability to hold these positions over the winter.
Trenches are not new to Ukraine. Trench warfare has long been a feature of the battle in eastern Ukraine for the Donbas region. Ukrainians fight from their own trenches on their side of the line near Popasna, where Russians are waging an intense campaign to dislodge Ukrainian troops from the city of Bakhmut.
But the pace and the scale of Russian construction over the past couple of months is unmatched.
The fortifications show how Russia's military is trying to set up more robust, defensible positions against Ukrainian pressure, often with the help of natural obstacles like rivers.
Last November, Ukraine recaptured a large amount of territory in the south, including the regional capital of Kherson, pushing Russian forces across the Dnieper River. The river serves as a natural barrier, and Russia has built an enormous series of defensive obstacles south of the river to discourage Ukraine from crossing it.
Among the defenses are miles-long rows of concrete pyramids known as dragon's teeth and deep ditches called tank traps. Both are designed to slow Ukrainian vehicles and force them into preset positions where Russian forces can target them.
Russia is also building miles of trenches, and pillboxes — small structures for their troops to shoot from.
The fortifications could slow Ukraine's army — but they are effective only if manned correctly.
If the positions are unmanned, they are useful only if there is an orderly Russian retreat, one of the most difficult tactical operations to conduct, said Philip Wasielewski, a fellow at the Foreign Policy Research Institute.