The baboons had been living in the zoological gardens at the Citadel of Besancon in western France for 40 years, The Local.fr reported.
"They don't do anything out of the ordinary. Just like in the wild they tinker with things and pull at the grass, but then they started to pull out small stones at the joints in the wall. And you have to remember we are a [United Nations Educational, Scientific and Cultural Organization] World Heritage Site," said Gerard Galliot, director of the Museum of Natural History, which houses the zoo. "Everything is still standing, the walls of the Vauban citadel have held out for many centuries, but these baboons are just not used to these places."
The Citadel of Besancon was built in the 17th century by military architect Vauban. It was named a World Heritage site in 2008 and is visited by about 250,000 tourists each year.
Along with the zoo, the citadel houses an aquarium, botanical gardens and a children's farm.
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