As NPR tells it, archaeologist Gary Feinman was "simply walking around eastern China's Shandong province" on a hunt for pottery shards when he found something much, well, greater: a rammed earth wall that reached as high as 15 feet in places. That there had been a wall built in Shandong in roughly 500 BC was not an entirely unknown fact. But Feinman was still rattled by what he saw, a surprisingly well-designed wall that "really runs along the higher ridge-tops of these very craggy mountains. ... In the upper reaches of its run, it was amazingly well preserved." And so Feinman set out to do what no one before him had: map it.
His suspicion is that it could be as many as several hundred miles long. "Nobody has seen how it snaked ... through such a large area," he says. And as NPR explains, its construction was fairly impressive, with countless tons of "fine-grained soil" being carted to higher elevations, where it was beaten into mounds firm enough to persist until present day. The "Great Qi Wall" was built under the Qi dynasty, as a form of protection from other regional Chinese dynasties. Qin Shi Huang eventually conquered all of China's regional states, bringing them together as one in 221 BC. It was Qin who began construction of a wall that became what is now the Great Wall. NPR has photos of the Great Qi Wall.