Peter Thiel, the U.S. billionaire venture capitalist and early supporter of U.S. President Donald Trump, launched on Sunday a series of closed-door lectures in Rome exploring the concept of the Antichrist, drawing scrutiny from Catholic commentators.

The invitation-only conference, which runs until Wednesday, is not open to the press and its venue has not been publicly disclosed. Organizers quoted in the media say participants are drawn from academia, technology and religious circles.

A co-founder of Palantir Technologies, an artificial intelligence software company with deep ties to the U.S. defense and intelligence agencies, Thiel has in recent years devoted increasing attention to religious and philosophical ideas.