Locations:
Egypt is most famous for pyramids, built around 4,500 years ago, but Mexico has the 1st and 3rd largest pyramids, Sudan has more pyramids (220) and there were also pyramids in Mesopotamia, Greece and China.
The Meso-American pyramids (Mexico, central and south america) were built starting around 3000 years ago.

Egyptian Pyramids:
There are 118 pyramids discovered in Egypt as of 2008. Most were built as tombs for the country's Pharaohs and their consorts during the Old (2575-2150 B.C) and Middle (1975-1640 B.C.) Kingdom periods, near the ancient capital of Memphis, south of present day Cairo.
Khufu's Great Pyramid at Giza (also known as the Pyramid of Cheops or Khufu) was built at the beginning of the Old period.

The tomb of Tutankhamun, a relatively minor king, is known better then any other, because of all the royal tombs, it was found mostly intact. It is a tomb 12 ft high not a pyramid, in the valley of the kings.

Somewhat abruptly the kings of the New Kingdom (1539-1075 B.C.) chose, rather than making their tombs completely obvious, to hide them in the hills of the West Bank of Thebes (modern Luxor), Valley of the Kings.
The valley is known to contain 63 tombs and chambers (ranging in size from a simple pit to a complex tomb with over 120 chambers.

Smaller pyramids were constructed, for example in the Deir el-Medina necropolis, a workers village just south of the Valley of the Kings, by private individuals.

Design - size:
The first Egyptian pyramid was the Step Pyramid at Saqqara, built for King Zoser in 2750.
The oldest pyramids, dating from 3,000BC, were in Brazil and about 160 feet high.



The largest Egyptian pyramid (Great Pyramid), built for the Pharaoh Khufu (whom the Greeks referred to as Cheops) at Giza around 2530 B.C. and intended to last an eternity, was until early in the twentieth century the biggest building on the planet. 86 Million cubic feet.
It's 756 feet long on each side, 450 feet high and is composed of 2,300,000 blocks of stone, each averaging 2 1/2 tons in weight. [The World Trade Centers 1 & 2 were 208 ft x 208 ft x 1368 (59 Million cubic feet)]
Great Pyramid of Cholula, in Mexico is 1476x1476 ft by 180-200 ft high for 157 million cubic feet.
The Boeing Plant in Everett, WA is 472 million cu ft.

To raise it, laborers moved into position six and a half million tons of stone some in blocks as large as nine tons with nothing but wood and rope.

Each pyramid consisted of an inner chamber that entombed the deceased, the servants of the deceased, and artifacts to make living in the afterlife similar to what they were used to every day. Servants, horses, and pets were buried with the deceased.

Originally, the pyramid itself was encased in highly polished white limestone with a smooth surface which is now gone. At the very top of the structure would have been a capstone, bringing the total height to 480 feet, which is also now missing. Some sources suggest that the capstone might have been sheathed in gold.

Who built them:
Egyptologist Mark Lehner, an associate of Harvard's Semitic Museum, is beginning to fashion an answer. He has found the city of the pyramid builders. They were not slaves.
Lehner currently thinks Egyptian society was organized somewhat like a feudal system, in which almost everyone owed service to a lord. The Egyptians called this "bak." Everybody owed bak of some kind to people above them in the social hierarchy. "But it doesn't really work as a word for slavery," he says. "Even the highest officials owed bak."

Estimates for the number of workers have ranged widely from the 100,000 cited by Herodotus, the 5th century B.C. Greek historian, to just the few thousand. Current estimates are a permanent work force of 4 to 5,000 men that at times increased to 40,000 with an average workforce of 13,200, built it over a 10 to 20 year period.


Mesoamerica pyramids:
Early civilizations in Mesoamerica (Mexico, Central and South America today) also built pyramids which were usually stepped and had flat tops where ceremonies and sacrifices were performed. The Maya also had pyramid-like structures for interment for powerful rulers.

Great Pyramid of Cholula, in the Mexican state of Puebla, is the world's largest monument and largest pyramid by volume. It was discovered in 1910 under what appeared to be a hill and still remains largely covered.

It was built in four stages, starting from the 3rd century BCE through the 9th century CE is 1476x1476 ft by 180-200 ft high for 157 million cubic feet. Little is known about its ancient builders, including their name. The Toltec-Chichimecas occupied Cholula c. 1100 A.D. By that time the great pyramid was already largely submerged underneath tree and dirt. In 1359, the kingdom of Huexotzingo (enemies of the Aztecs) took over Cholula. About 100 years later the Aztecs took over and believed that the God Xelhua built the Great Pyramid of Cholula.
In 1519 Cortés massacred thousands as as part of Spain's effort to collonize Mesoamerica. Apparently he never noticed the buried pyramid. The Spanish built a church on top of the mound over the pyramid.

Because of the historic and religious significance of the church on the top of the mound over the pyramid, which is a designated colonial monument, the pyramid as a whole has not been excavated and restored, as have the smaller but better-known pyramids at Teotihuacan.
There is a vast network of tunnels allowing you to see parts of the structure underneath.

Links:
Pyramid at Wikipedia
National Geographic: Egypt Pyramids--Time Line
Seven Wonder of the Ancient World: Khufu's Great Pyramid
NOVA Online/Pyramids/Who Built the Pyramids?
The Great Pyramid at scribd.com
Pyramids in Egypt- Map
CULTUREFOCUS: Ancient Egypt. Pyramids of Giza, pictures and history.
BBC - History: Egyptians
Meso-American pyramids
Afterlife:
Ancient Egyptian religion - Wikipedia, the free encyclopedia
Ancient Egyptians


last updated 25 Aug 2009