The UK Defense Ministry said in November that two factories were producing concrete “dragons’ teeth” tank obstacles.

These defenses began to appear after Russian forces withdrew from part of Kherson region in November, and essentially established a new defensive line stretching across largely rural areas of southern Ukraine. The Russian-appointed head of Crimea, Sergey Aksyonov, said earlier this month that “our armed forces have built a modern, deeply-echeloned defense.” Maxar’s Stephen Wood says these defenses are replicated across a huge stretch of territory, from Crimea in the south all the way to parts of Donetsk.ĬNN has previously reported on defensive fortifications being built in north Crimea. This area will be critical should Ukrainian forces try to advance towards the city of Melitopol and split Russian forces in the south. Russian defenses included, for example, anti-tank ditches near Polohy stretching for 30 kilometers (19 miles), as well as extra fortifications around important towns like Tokmak. Satellite images showing defensive trenches in the Zaporizhzhia region. They showed that “Russia’s positions are most concentrated near the front lines in the south-eastern Zaporizhzhia region, in the east and across the narrow strip of land connecting the Crimean Peninsula to the rest of Ukraine,” according to the Reuters analysis. A Reuters’ analysis of imagery found thousands of defensive positions over a vast area. Several satellite images shared with CNN by Maxar Technologies, and taken on Wednesday, show extensive trenches east of the town of Polohy in Zaporizhzhia region. The challenge for the Ukrainians will be to bypass or overcome such obstacles at speed, creating momentum that causes Russian command and control to melt down. The defenses continue for hundreds of miles across the meandering southern front – where Ukrainian forces are expected to concentrate their counter-offensive in the coming weeks.

Satellite imagery reviewed by CNN and other news organizations shows the extent of Russian defenses that have been built up in parts of southern Ukraine – layers of anti-tank ditches, obstacles, minefields and trenches.

Breaking through will present a huge challenge. But the Russians have had nearly six months to prepare the ground – and build an elaborate array of defenses. When it’s launched, probably in the south, it will mark a pivotal moment in the conflict. Ukraine says its preparations for a spring counter-offensive are almost complete.

The longest day a bridge too far