Angkor Wat may be covered in graffiti—but don’t worry, it’s invisible. Built in the early 12th century, Cambodia’s architecturally iconic temple is known for its intricate carvings, some of them stretching nearly a kilometer in length. But most archaeologists believe that parts of the temple were once painted as well. So when scientists noticed faint traces of red and black pigment on the walls of several rooms in Angkor Wat, they snapped pictures with a bright flash and used a tool called decorrelation stretch analysis to digitally enhance the images. Previously used to highlight subtle color differences in images of the martian landscape taken by NASA’s Opportunity rover, this type of analysis can reveal colors too faint or faded to be seen with the naked eye. When the researchers applied it to their photos of Angkor Wat, they found more than 200 images of boats, deities, buildings, and animals—like the elephants above (inset)—drawn on the walls throughout the temple, they report today in Antiquity. Most of the paintings are haphazardly arranged and appear to be graffiti left by visitors after Angkor Wat was first abandoned in 1431. But one group of carefully drawn scenes, located in the highest tier of one of Angkor Wat’s towers, might be the remains of a 16th century restoration program, when the complex was transformed from a Hindu temple into a Buddhist shrine. The previously lost images could give archaeologists new insight into this little-known period in Cambodia’s history.