Collectively, the factory facilities identified by BuzzFeed News cover more than 21 million square feet — nearly four times the size of the Mall of America. (Ford’s historic River Rouge Complex in Dearborn, Michigan, once the largest industrial complex in the world, is 16 million square feet.)

And they are growing in a way that mirrors the rapid expansion of the mass detention campaign, which has ensnared more than 1 million people since it began in 2016. Fourteen million square feet of new factories were built in 2018 alone.

Two former detainees told BuzzFeed News they had worked in factories while they were detained. One of them, Gulzira Auelhan, said she and other women traveled by bus to a factory where they would sew gloves. Asked if she was paid, she simply laughed.

The former detainees said they were never given a choice about working, and that they earned a pittance or no pay at all. “I felt like I was in hell,” Dina Nurdybai, who was detained in 2017 and 2018, told BuzzFeed News. Before her confinement, Nurdybai ran a small garment business. At a factory inside the internment camp where she was held, she said she worked in a cubicle that was locked from the outside, sewing pockets onto school uniforms. “They created this evil place and they destroyed my life,” she said.