Scientists had long thought it was a myth, but new evidence has emerged that an ancient flood in China was very, very real. The myth claims a flood threatened the heavens themselves some 4,000 years ago, blasting through a large part of central China and wiping cities from the face of the Earth.

The flood even led to the myth of a hero named Yu the Great, wo spent decades digging canals to channel the floodwater, and was supposedly the emperor of the Xia Dynasty, China’s first dynasty. But researchers have found that there may be some truth to it — at least the flood part, according to an American Association for the Advancement of Science statement.

The researchers have found evidence of a tremendous flood that may have happened along the Yellow River. Archaeologists and geologists found evidence that the river had been dammed up in a place known as the Jishi Gorge, probably by a huge earthquake and subsequent mud slide. It would have been bigger than the Hoover Dam, and if it had suddenly failed, it would have sent 3.8 cubic miles of water that could have traveled 1,250 miles.

That would have made it the biggest flood on Earth in the last 10,000 years, 500 times larger than a typical Yellow River flood from rainfall.

The researchers discovered this by examining sediments from the Jishi Gorge about 16 miles downstream. Radiocarbon dating showed that they were 3,900 years old, around the same time that it happened.

“Researchers have provided geological evidence for China’s “Great Flood,” a disastrous event on the Yellow River from which the Xia dynasty is thought to have been born,” the statement reads. “The flood occurred in roughly 1920 BC, they say, which is several centuries later than traditionally thought – meaning the Xia dynasty, and its renowned Emperor Yu, likely had a later start than Chinese historians have thought, too. According to Chinese legend, Emperor Yu gained notoriety through his handling of the country’s Great Flood.

“Here, by reconstructing a sequence of events along the Yellow River – including a landslide that created a dam from which water built up and burst forth — Wu Qinglong and colleagues provide geological evidence for a catastrophic flood event that may be the basis of the Great Flood,” the statement continues. “The researchers mapped and dated distinctive sediments that were deposited downstream of a Qinghai Province dam when the dam broke. In further work, they determined that the flood that broke the dam was of enormous proportions. … Taken together, these results reveal how the concurrence of these major natural and sociopolitical events may be an illustration of a profound and complicated cultural response to an extreme natural disaster that connected many groups living along the Yellow River.”