Aside from animals, Darwin’s Arch is one of the most famous, and most photographed, things on the Galapagos Islands. As of May 17, it has permanently changed a little: The arch collapsed into the ocean, leaving behind two solitary unconnected pillars.

In a tweet, the Ministry of Environment for Ecuador reported that the cause of the collapse was erosion — a natural process and not one connected to human interference or overtourism. The huge rock formation (141 feet high, 230 feet long, and 75 feet wide), takes its name from the iconic naturalist who found much of the inspiration for his theories of evolution from his travels around the Galapagos Islands.

The rock formation is located near Darwin Island, and while the islet is not open to visitors, CNN reported that it’s considered one of the best diving spots in the archipelago because whale sharks, hammerhead sharks, and manta rays tend to gather nearby.

There were witnesses to the incident. A tour boat called the Galapagos Aggressor III, run by a tour company called Aggressor Adventures, shared a post on Facebook claiming that one of its tour groups had actually seen the collapse take place.

“This morning at 11:20 a.m. local time, the world famous Darwin’s Arch collapsed in front of their eyes,” part of the post reads. The company went on to say that within the travel industry, the rock formation has taken on a new nickname: the Pillars of Evolution.