As many as 70 artifacts housed in the five museums of Berlin’s Museum Island have been sprayed with a mysterious oily liquid in what is being described as the biggest attack on art and antiquities in post-war Germany, the BBC reports. The attack took place on Oct. 3, the anniversary of German reunification, causing authorities to speculate whether the attackers may have been supporters of the far-right conspiracy theorist called Attila Hildmann, who has claimed that the Pergamon Museum on the site is home to the original “throne of Satan.” Authorities chose to keep the attack quiet until late Tuesday, when they were confronted by German media outlets that had been told of the attack after museum directors emailed patrons who had visited the museums on the day of the attack. It is unclear why the attack was kept secret.