Archaeologists in Alabama have discovered the longest known painting created by early Indigenous Americans, a new study finds. Indigenous Americans crafted this 1,000-year-old record-breaking image — of a 10-foot-long (3 meters) rattlesnake — as well as other paintings, out of mud on the walls and ceiling of a cave, likely to depict spirits of the underworld, the researchers said.

The cave has hundreds of cave paintings and is considered the richest place for Native American cave art in the American Southeast, the researchers said. To investigate its historic art, the team turned to photogrammetry, a technique that involves taking hundreds of digital images in order to build a virtual 3D model. Using this method, the researchers spotted five previously unknown giant cave paintings, known as glyphs.

"This methodology allows us to create a virtual model of the space that we can manipulate," study first author Jan Simek, a distinguished professor in the Department of Anthropology at the University of Tennessee, told Live Science. "In this particular case, the ceiling of the cave is very close to the floor. So your field of vision is limited by your proximity to the ceiling. We never saw these very large images because we couldn't get back far enough to see them."

After creating the virtual model, "we could look at it from a greater perspective," he said. "It allows us to see things in a way that we can't in person."

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The record-setting glyph sports a diamond pattern, indicating that it may depict a diamondback rattlesnake (Crotalus atrox), a creature considered sacred by the Indigenous peoples of the American southeast, the researchers said. These peoples constructed large earthen mounds, used for a variety of purposes, including rituals according to Smithsonian Magazine, and to be closer to the spirits of the upper world, while caves were viewed as the opposite — routes to the underworld.

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"These are special because until now, we have had no large figures from this area," Simek said "And so that changes our perspective on what might be in these caves." For instance, there are similarly large rock art images made by Indigenous peoples in the western United States, although these glyphs are not found in caves, he said. "It brings the cave art of the southeast into the discussion of other monumental images that we see in different parts of North America," Simek noted.

This cave was first discovered in 1998 and remains unnamed, going by the moniker "19th unnamed cave" in order to protect the discoveries. The cave contains over 3 miles (5 kilometers) of underground passages with the majority of paintings discovered in one large chamber, according to a 1999 study published in the journal Southeastern Archaeology. In continuing to use photogrammetry techniques on the 19th unnamed cave and others, the team hopes to further improve understanding of Indigenous American art.

The study will be published online Wednesday (May 4) in the journal Antiquity.

Originally published on Live Science.