Researchers in Italy have warned that Michelangelo's David is at risk of toppling, and they say its ankles are to blame. The celebrated marble sculpture, housed at a museum in Florence, stands at about 17 feet and weighs over 12,000 pounds. It's remained largely intact for more than 500 years, but tiny cracks in its ankles may threaten its stability, according to recent findings from Italy's National Research Council (CNR), published in the Journal of Cultural Heritage.

Experts have long said that David is at risk of collapsing due to the poor-quality marble that Michelangelo used, as well as its precarious pose. Because of these structural problems, an earthquake or even vibrations from nearby construction could cause it to fall. To test its stability, researchers from CNR and the University of Florence created small plaster replicas of the sculpture and exposed them to forces stronger than gravity inside a centrifuge. Based on their results, they believe the ankle micro-fractures developed after years of outdoor exposure in a public square, where it leaned forward at an angle of about five degrees. David was put on public display outside a Florentine government building in 1504, when it was first unveiled, before being moved inside the Accademia Gallery in 1873.

The cracks have been covered in plaster in the past, only to resurface later. It's not yet clear whether efforts to stabilize the work are underway, though some have called for it to be moved to an earthquake-proof room, away from Florence's busy city center.