What do you picture when you think about ancient Egypt? Pharaohs? The Nile River? The desert? A sphinx? Mummies?

Of course, all of these things are lasting images of ancient Egypt. But some of the most popular images associated with ancient Egypt are of pyramids.

Pyramids have been built in many countries around the world. For example, Sudan has over 200 pyramids — the most of any country in the world.

Egypt, however, contains the most famous ancient pyramids. Built thousands of years ago as tombs for pharaohs (Egyptian leaders) and their families, over 130 pyramids have been discovered throughout Egypt.

Pyramids have a unique geometric shape. In geometry, a pyramid is defined as a polyhedron made by connecting a polygonal base (a two-dimensional shape with three or more straight sides) with a point at the top, called the apex.

The base of a pyramid can be a triangle, a square, a rectangle or other shapes with even more sides. Each side of a pyramid (each base edge and the apex) forms a triangle.

The Egyptian pyramids may have been modeled after a sacred, pointed stone called the ben-ben. The ben-ben stone represented the rays of the Sun, and ancient Egyptians believed that pharaohs who died reached heaven on sunbeams.

The shape of a pyramid allows weight to be distributed evenly throughout the structure. Most of the weight in a pyramid is on the bottom and it decreases the higher you go. This allowed ancient civilizations to create huge structures of stone that were very sturdy.

The most famous Egyptian pyramids are located at Giza near Cairo. The pyramids at Giza are some of the largest structures ever built. The Great Pyramid of Khufu at Giza is the tallest pyramid in the world. It's also the only one of the Seven Wonders of the Ancient World still in existence.

The Great Pyramid of Khufu is built of over 1.3 million huge limestone blocks that weigh anywhere from 5,000 pounds to over 30,000 pounds. Its four sides face north, south, east and west precisely.

It was originally 488 feet tall, but today it stands only 455 feet. The missing 33 feet were high-quality casing stones that were removed long ago to build houses and mosques in Cairo. You may have noticed some of these missing outer stones in the photograph of the Great Pyramid of Khufu.

No one knows for sure exactly how the pyramids were built. Without modern machines and building techniques, the ancient Egyptians managed to create architectural masterpieces that still baffle scientists today.

One thing is certain, however: it had to take a tremendous amount of manpower to create the pyramids. Some experts believe the pyramids could have been built with as few as 20,000-30,000 workers. Other experts, however, argue that it might have taken over 100,000 workers!

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