Researchers just discovered the world’s largest underwater cave

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By linking two existing underwater-cavern systems on the Yucatan peninsula of Mexico, near the beach resort of Tulum, researchers and professional cave divers have established the world’s largest underwater cave.

The discovery of the connecting tunnel brought together the cave known as Sac Actun, measured at 263 km, with the 83-km Dos Ojos cave, creating a single 347-km (216-mile) passage. According to spelunking protocol, when two caves are connected, the entire system takes on the name of the larger cave. In other words, Dos Ojos is no more; it’s now a part of Sac Actun.

The link was discovered following months of exploration by a diving team led by Robert Schmittner, a professional cave diver who has been studying the Yucatan caves for years. Researchers had long believed that several of the cave systems on the peninsula were connected, but until now no one had actually found, let alone swimmed through, a connection.

The effort is part of a project called the Gran Acuifero Maya, which seeks to preserve and study the vast, labyrinthine cave systems of the Yucatan. Guillermo de Anda, the project’s director, says the new discovery also provides new insights into Mayan civilization as it existed before contact with Spanish conquistadors. The divers found artifacts, like ceramic pots, in the caves, as well as human bones and the remains of now extinct animals.

The ancient Mayans were known for conducting religious sacrificial ceremonies around the caves, which are known locally as “cenotes,” and the new discoveries may improve historians’ understanding of a culture that reached the peak of its power near the sixth century AD.