A technique called decorrelation stretch analysis, which exaggerates subtle color differences, revealed images like this one showing two elephants facing each other.

Each year, millions of visitors flock to Angkor Wat, an ancient temple in modern-day Cambodia. There, they marvel at the 900-year-old towers, a giant moat and the shallow relief sculptures of Hindu gods. But what they can't see are 200 hidden paintings on the temple walls.

New, digitally enhanced images reveal detailed murals at Angkor Wat showing elephants, deities, boats, orchestral ensembles and people riding horses — all invisible to the naked eye.

Many of the faded markings could be graffiti left behind by pilgrims after Angkor Wat was abandoned in the 15th century. But the more elaborate paintings may be relics of the earliest attempts to restore the temple, researchers said. [See Photos of Angkor Wat's Secret Paintings]

Painting discovery

Subtle traces of paint caught the eye of Noel Hidalgo Tan, a rock-art researcher at Australian National University in Canberra, while he was working on an excavation at Angkor Wat in 2010.

Built between A.D. 1113 and 1150, Angkor Wat stood at the center of Angkor, the capital of the Khmer Empire. The 500-acre (200 hectares) complex, one of the largest religious monuments ever erected, originally served as a Hindu temple dedicated to the god Vishnu, but was transformed into a Buddhist temple in the 14th century.

Built between roughly A.D. 1113 and 1150, and encompassing an area of about 500 acres (200 hectares), Angkor Wat, whose name means "temple city," is one of the largest religious monuments ever constructed. (Image credit: Noel Hidalgo Tan)

Tan said he kept spotting traces of red pigment all over the walls when he was taking a stroll through the temple on his lunch break one day. He took a few pictures and planned to digitally enhance them later.

"I didn't realize that the images would be so detailed, so I was naturally taken aback," Tan told Live Science in an email.

The digitally enhanced pictures revealed paintings of elephants, lions, the Hindu monkey god Hanuman, boats and buildings — perhaps even images of Angkor Wat itself. Tan went back to the site to conduct a more methodical survey in 2012 with his Cambodian colleagues from APSARA (which stands for the Authority for the Protection and Management of Angkor and the Region of Siem Reap).

Invisible images

"Some of the most detailed paintings, the ones located at the top of the temple, are passed by literally thousands of visitors every day, but the most elaborate scenes are effectively invisible to the naked eye," Tan said in an email.

To make these paintings visible, Tan used a technique called decorrelation stretch analysis, which exaggerates subtle color differences. This method has become a valuable tool in rock-art research, as it can help distinguish faint images from the underlying rock. It has even been used to enhance images taken of the Martian surface by NASA's Opportunity rover.

One chamber in the highest tier of Angkor Wat's central tower, known as the Bakan, contains an elaborate scene of a traditional Khmer musical ensemble known as the pinpeat, which is made up of different gongs, xylophones, wind instruments and other percussion instruments. In the same chamber, there's an intricate scene featuring people riding horses between two structures, which might be temples. [Image Gallery: How Technology Reveals Hidden Art Treasures]

One chamber in the highest tier of Angkor Wat's central tower, known as the Bakan, contains an elaborate scene of a traditional Khmer musical ensemble known as the pinpeat, which is made up of different gongs, xylophones, wind instruments and other percussion instruments. (Image credit: copyright Antiquity)

"A lot of the visible paintings on the walls have been previously discounted as graffiti, and I certainly agree with this interpretation, but there are another set of paintings discovered from this study that are so schematic and elaborate that they are likely not random graffiti, but an attempt to decorate the walls of the temple," Tan said.

Christophe Pottier, an archaeologist and co-director of the Greater Angkor Project who was not involved in the new study, agreed that these more complex murals show deliberate intention and can't be interpreted as mere graffiti.

Pottier, however, added that the discovery of hidden paintings isn't all that surprising. Though they haven't been studied systematically before now, several traces of paintings have been found at the temple during the last 15 years.

"But I am very pleased, because the traces identified are quite diverse, lively and original," Pottier said. Most of the paintings that were previously known depicted boats and floral and geometric designs, Pottier told Live Science in an email.

Though researchers don't know exactly when the paintings were created, Tan speculated that the most elaborate artworks may have been commissioned by Cambodia's King Ang Chan, who made an effort to restore the temple during his reign between 1528 and 1566. During this time, unfinished carvings were completed and Angkor Wat began its transformation into a Buddhist pilgrimage site. Some of the newly revealed paintings have Buddhist iconography, such as a painting of a temple that looks like a Buddhist mound-like monument known as a stupa.

The findings were detailed in the journal Antiquity this week.

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