1 . For centuries, people wondered how big the Earth was. Unfortunately, although the Earth was flat, no one was able to figure out its size. Gradually, however, people began to realize that the Earth was really round.

Then, in the third century BC (2,300 years ago), a Greek man named Eratosthenes had an idea. Eratosthenes was sure that the Earth was a sphere. He used the sun and geometry (几何学) to figure out the size of the Earth. He calculated that the circumference (圆周) of the Earth was 28,600 miles (46,000 kilometers). The true size of the Earth is 25,000 miles (40,000 kilometers).

Eratosthenes’ measurement was wrong, but it was very close to the truth.

For many centuries after Eratoshenes lived, people made maps of the Earth. However, they did not know very much about the world outside of Europe, Asia, and North Africa. Mapmakers could not draw accurate maps of the Earth until people began traveling around the world in the fifteenth century, mapping small areas each time. In the eighteenth and nineteenth centuries, people began making correct maps of countries, but the first accurate maps of the world were not made until the 1890s.

Maps today are reliable (可依靠的), inexpensive, and easy to understand. People depend on maps every day. What would our lives be like without them?