PARIS (AP) — The oldest bridge in Paris looked Thursday as if it had been swallowed by a mountain.

The transformation is the work of JR, the street artist known as the “French Banksy,” who this week began inflating a giant artificial “cave” over the Pont Neuf, turning the 17th-century bridge that has carried Parisians across the Seine for more than 400 years into a rocky illusion rising over the river.

JR has said the idea of La Caverne du Pont Neuf is to bring “mineral and nature” back to the heart of the city. He says he is not covering the bridge so much as revealing the stone taken from limestone quarries from which Paris itself was cut.

A jagged mass of gray rock now seems to rise over its arches. From downstream, the landmark appears to have vanished beneath a prehistoric cliff, its stone openings transformed into dark cave mouths above the water.

“I thought, ‘Where has the bridge gone?’” said Marie Leclerc, 62, who stopped on the quay on her way to work. “It’s strange because you know it’s fabric and air, but from here it really looks like stone. Paris feels suddenly ancient again.”