 The Russians are accelerating their preparations for a Ukrainian counter-attack. The anti-tank ditches near Ukraine's occupied south-eastern town of Polohy stretch for 30 kilometres, behind our rows of concrete, dragon's teeth barricades. Further back are defensive trenches where Russia's troops will be positioned. Tens of thousands of Ukrainian troops have been training in the west to use different military assets on the battlefield in a combined way. Ahead of a counter-offensive, Ukrainian officials say will come when its forces are ready. Reuters has reviewed satellite images of thousands of defensive positions inside both Russia and along Ukrainian front lines that show it is most heavily defended in the southern Zaporosia region and the gateway to the Crimean peninsula. Six military experts said the defence, mostly built in the wake of Ukraine's rapid autumn advances, could make it harder for Ukraine next time and that progress would hinge on its ability to carry out complex, combined operations effectively. A Ukrainian counter-offensive could change the dynamics of a war that has slowed into a bloody battle of attrition and military experts say the length of the front at about 1,200 kilometres could stretch Russia's defences. Stretching hundreds of kilometres, the military experts say the defences mark areas where Russia expects to be attacked or seize strategic significance in holding onto territory. According to the satellite images, Russia's positions are most concentrated near the front lines in the southeastern Zaporosia region in the east and across the narrow strip of land connecting the Crimean peninsula to the rest of Ukraine. They're trying to limit Ukrainian movement. So what the Ukrainians will seek to do in their offensive is to pierce the Russian line and then rapidly drive their military vehicles to the coastline or into rear areas. And so the length and the width of these defences is structured to prevent that. So you have the front, you have the ditch, which is to stop armored vehicles or to at least make it difficult for them to advance. Then you run into the dragon's teeth or devil's teeth, which is another tool to make it harder for them to advance. And then only then will you encounter the primary defensive trench, which is where the Russians will be presumably shooting at them the whole time. Russians have the river on one side, they have the ocean at their back, and in a way that traps them, but it also allows them to concentrate their defences because fortifications like this with earth-moving technology, they're not necessarily hard to install, but if you've ever dug a ditch of any size, you know that it's a great deal of effort. And so when you have a kind of area like this that you know you must defend that's a little bit smaller thanks to geography and thanks to the overall stabilization of the front, it makes sense and is possible to create defenses like this in order to restrict Ukrainian movement. And I think that that's true, that that's more evidence of the way that the war has stabilized and the way that the war going forward is going to be, in a sense, less dramatic at like the strategic or macro scale, but in a lot of ways more dangerous for the people involved. This is an age of war in Europe that was thought to be over, and so we're kind of going back to this kind of conflict. And I think that the scale would be interesting and remarkable. The Russians have quite a lot of territory to defend in terms of this area all the way from the Niber eastwards, and they're aware of it.