This is the first of a series of seven looks at the seven wonders of the world. The list was started in the second century BC and the wonders we know today were finalized in the Middle Ages. Only one still in existence, after some 4,500 years, and visible today is the great pyramid of Khufu at Giza in Egypt. It is 756 feet long on each side, 450 high and comprises 2,300,000 blocks of stone, each averaging 2 1/2 tons in weight.

Despite not having the scientifically accurate instruments of today, no side is more than 8 inches different in length than another, and the whole structure is perfectly oriented to the points of the compass. It seems likely that the pyramid was a tomb for a Pharaoh. Even in ancient times, thieves, breaking into the sacred burial places, were a major problem and Egyptian architects became adept at designing passageways that could be plugged with impassable granite blocks, creating secret, hidden rooms and making decoy chambers. No matter how clever the designers became, though, robbers seemed to be smarter and with almost no exceptions each of the great tombs of the Egyptian Kings were plundered.

Until the 19th century, the pyramid of Khufu was the tallest building in the world. A Greek traveller called Herodotus of Halicanassus visited Egypt around 450 BC and included a description of the Great Pyramid in a history book he wrote. Herodotus was told by his Egyptian guides that it took 100,000 slaves twenty-years to build the pyramid.

The site was first prepared, and blocks of stone were transported and placed. An outer casing (which has disappeared over the years) was then used to smooth the surface. Although it is not known how the blocks were put in place, several theories have been proposed. One theory involves the construction of a straight or spiral ramp that was raised as the construction proceeded. This ramp, coated with mud and water, eased the displacement of the blocks that were pushed (or pulled) into place. A second theory suggests that the blocks were placed using long levers with a short angled foot. Stones were lifted into position by the use of immense machines. The purpose of the structure, according to Herodotus's sources, was as a tomb for the Pharaoh Khufu (whom the Greeks referred to as Cheops). Scientists have since calculated that fewer men and less years were needed than Herodotus suggests.

Next month: the Lighthouse at Alexandria