The Great Wall of China, built more than 2,000 years ago, stands as one of the monumental feats of ancient engineering. Stretching thousands of miles, it protected the newly unified country from foreign invaders.

But before the Great Wall, warring Chinese dynasties built many other walls for protection. An American archaeologist recently began surveying one of the biggest.

Gary Feinman, who is with the Field Museum of Chicago, didn't set out to excavate what he now calls "the first Great Wall." He was simply walking around eastern China's Shandong province, staring at the ground like any good archaeologist, looking for tiny pieces of pottery.

But two years ago, he came across an earthen wall. In some places, it was 15 feet high. People knew there had been an early great wall in Shandong, dating to about 500 B.C. — built centuries before the Great Wall. What Feinman discovered seemed to be a part of that early wall. "By walking this part ... we have seen how well designed it was," he says. "It really runs along the higher ridge-tops of these very craggy mountains in eastern Shandong. In the upper reaches of its run, it was amazingly well preserved."...