The Longyou Caves are among the most mysterious ancient sites in world history. Built around 2,000 years ago, these human-crafted caverns lay in obscurity for centuries until they were accidentally discovered by farmers in the 1990s.
The sandstone caves are located near the village of Shiyan Beicun on the Qu River in Zhejiang province, eastern China. The caves were found in 1992 when local farmers drained several ponds revealing five large caverns. Later work then revealed a further 19 smaller caves at the site.
As a 2009 study notes, the 24 caves come in varying sizes, ranging from 18 to 34 meters (59 to 111 feet) in width and 8 to 18 meters (26 to 59 feet) in height, complete with lofty slanted roofs and amazingly solid pillars.
In the years following its discovery, archaeologists from China, Japan, Poland, Singapore, and the US flocked to the scene. The caves were found to contain historical relics from the reign of Emperor Xuan of Han who lived from 91 to 48 BCE, suggesting the cave was forged by humans over 2,000 years ago.
The age was gobsmacking. Experts struggled to explain how the caves managed to maintain their integrity for more than 2,000 years. Furthermore, any armchair archaeologists can point out that these certainly don’t look like many structures created 2,000 years ago.
Looking at the stripes in the cave walls, we can guess that they were somehow built by chiseling away at the ground layer by layer, but there’s little idea of how the caves were constructed. Indeed, no ancient records of the caves or their construction have ever been recovered.
Perhaps the only structures similar to the Longyou Caves are the Huashan Grottoes, but these are found 200 kilometers (120 miles) away in another pocket of China and were likely built 1,500 years later.
It’s also a mystery why ancient people went to such great lengths to create these caverns. Was this a shelter, a military bunker, a ceremonial structure, a secret palace of the elites, or a mine for natural resources?
One theory put forward in 2014 by Yang Hongxun, a researcher at the Institute of Archaeology of the Chinese Academy of Social Sciences, is that the caves were built under the command of the ancient king Goujian in 494 BC. According to Chinese media, Hongxun argues that Goujian used the caves to hide his thousands of soldiers following a crushing defeat in battle.
Truth be told, many aspects of the Longyou Caves remain a mystery, although one thing is fairly certain: it wasn’t aliens.