Lucy Catlin, age 11, of Charlotte, North Carolina, for her question:

How lone did it take to build the Egyptian Pyramids?

The Egyptians started building big stone pyramids more than 4,500 years ago. They built many of them. But goodness knows how many have long since disappeared in the shifting sand. The ruins of 35 still stand in the deserts around the Nile. The three largest of these ancient pyramids stand near Giza. Archeologists estimate that they were built between 2600 B.C. and 2500 B.C. If these figures are correct, these three massive tombs were all erected within a century.

The largest is the tomb of King Khufu. The Greek historian Herodotus wrote about it some 2,000 years ago. He stated that 400,000 Egyptians worked every day for 20 years to erect this biggest of all pyramids. Modern archeologists are not sure that these figures are correct but they cannot give a more accurate estimate. In any case, this pyramid required lots of time and toil. Its base covers 13 acres of ground. More than two million stone blocks were hoisted in place to build its sloping sides. Most of them wieghed around 2 1/2 tons. Originally its topmost point stood 481 feet above the base  ¬but time and weather have worn it down to 450 feet.