China has bulldozed the gravestones of Swedish missionaries credited with converting thousands of Chinese citizens to Christianity nearly a century ago.

Claiming the structures were “illegal,” on Sept. 12, over 100 special police and public security officers and personnel from various government institutions blocked a cemetery located in Yuncheng, according to Bitter Winter, an online magazine that focuses on religious freedom and human rights in China.

A short time later, three excavators were brought in to destroy the gravestones of 20 Swedish missionaries buried in the cemetery, along with the adjoining guest house, designating it, too, as an “illegal construction.” During the demolition, aerial drones flew overhead and monitored the destruction.

To conceal the demolition, government-hired personnel planted vegetation atop the ruins overnight. A government insider told Bitter Winter that all villagers living near the cemetery were summoned to the local police station prior to the demolition, and their cellphones were confiscated to prevent information leaks.

The demolished gravestones were established in 2008 to honor missionaries with the Swedish Mission in China.

The missionaries helped build 60 churches with over 6,000 members. They also established Yucheng Hospital, which residents could use for free. The hospital is credited with saving thousands of lives.