Shira Burack, age 10, of Downsview, Ontario, Canada, for her question:

Why did they build the Great Wall of China?

Human history, sad to say, is a long list of bloody wars and plundering invasions. About 1,000 years ago, Europe was terrorized by the plundering Vikings. About 2,000 years ago, Mongol tribes of the Gobi desert set forth on plundering raids into Europe and Asia. The Chinese called them Tartars. The Europeans borrowed this name because it was like their word for Hades, the mythical realm of dark terror.

Long before this, the Chinese had built several smallish walls to keep out invaders. About 589 A.D., they decided to join these in one long wall to keep out the Tartars. The enormous project took several centuries. But at last this Great Wall of China zig=zagged for 1,500 miles. Its sturdy stone sides stand 25 feet, sheltering a high road 15 feet wide. Every 200 or 300 yards there are higher fortified towers, where soldiers once watched and waited to defend China from the Tartars.