The fighting had become increasingly ferocious last month at the Zenith air-defense base a mile south of Avdiivka, where for years a company of Ukrainian soldiers had defended the southern approaches to the city.

Russian troops had moved up on their flanks and were pounding them from all sides with tank, artillery and mortar fire, smashing their defenses and wounding men.

“Every day we tried to repel enemy attacks,” said Senior Soldier Viktor Biliak, a 26-year-old with the 110th Mechanized Brigade, who had spent 620 days defending the base. “All the fortifications were being destroyed and there was no possibility to build new ones.”

Soldiers interviewed after their retreat described an uneven four-month battle under a relentless onslaught of Russian artillery and glide bombs that destroyed buildings and broke through deep concrete bunkers. As the Ukrainians took casualties they became increasingly outnumbered by the Russians assaulting the city, who broke through at two strategic points and quickly seeded areas with fighters.

The fall of the city, when it came in mid-February, was brutal and fast, occurring in less than a week.