25. Sergiyev Posad-6, a military site northeast of Moscow, was a Soviet biological weapons research center during the Cold War. The Soviet military used the lab to experiment with weaponizing the viruses that cause smallpox and Ebola, among others. Shortly after Russia launched its full-scale invasion of Ukraine in February 2022, satellite imagery indicated massive construction and renovation at the Sergiyev Posad-6 site, the WP reported, citing photos from imaging firms Planet Labs and Maxar. The expansion amounts to over 250,000 square feet and 10 new buildings. According to experts in biodefense, the military, and satellite imaging who spoke to the WP, the facilities harbor some of the distinctive features of high-security biological labs that handle dangerous pathogens. Among these features are extensive rooftop air handling units, underground infrastructure, heightened security, and a possible power plant.