What was the purpose of the pyramids? | AskHistorians Archive Observer

So already by the time of the first unification of Egypt by the Pharaoh Narmer in 3100 BCE there was a tradition of burying the dead inside a pit grave and then placing a rectangular mudbrick structure with slightly inleaning walls over this called a mastaba (literally "bench") to protect from scavenging animals and grave robbers. This type of tomb was reserved for royalty and high officials and often had accompanying shrines and temples for rituals to the dead.

In the 27th century BCE the architect Imhotep came up with the idea for the tomb of the Pharaoh Djoser to place a mastaba on top of a mastaba on top of a mastaba resulting in a six level structure 62m high with sides about 100m long known as a step pyramid. It was constructed within the 19 year reign of the pharaoh, made of stone and not mudbrick and is considered the earliest large scale cut stone construction.

The next big change was in the reign of the Pharaoh Sneferu (roughly 2613 BCE to 2589 BCE). He first decided to begin work finishing an incomplete second step pyramid in Meidum originally planned for his predecessor. He expanded the existing structure but then changed the design from being a step pyramid into a true pyramid by filling in the steps with limestone casing. Unfortunately the outer structure was founded on sand not rock and the structure collapsed before completion.

He then attempted to build another true pyramid from scratch in Dahshur. From a base around 190m this rose at an angle of 54 degrees, however this angle changes to 43 degrees after 47 meters and meets at a point 104m high. Its thought that the initial angle was far too steep and the change was made to avert collapse.

Finally he began another true pyramid at Dahshur, the Red Pyramid. This was the first successful true pyramid, and measured 220m on a side and 105m high, with an angle of 43 degrees.

So he managed to nearly finish 3 pyramids in his 30 year reign, which gives you some idea how much time it took for a pyramids construction.

His son, Khufu (2589–2566 BCE), went on to build the Great Pyramid at Giza. This too around 10-20 years to construct, was 230m long on a side and 146m tall with a 51 degree slope. It was the tallest structure on earth for 3800 years.

So I have no idea when the great flood was supposed to happen, but to give you an idea of timeframe, Ahmose I (1550–1525 BC) is considered to be the Exodus pharaoh, and the pyramids had been standing 1000 years by his reign.

They were not built by slaves. Egypt's agriculture was entirely based around the yearly inundation of the Nile, where the river would rise up to 14m and cover the Nile valley with a fresh layer of topsoil. So from about September to January all farmland was underwater. This leaves a huge idle workforce which could be mobilized for construction projects. In addition to these tens of thousands of farmers there were several thousand specialists and skilled workers hired permanently.

As far as why they were built. I have never heard anything to convince me that they were anything more than tombs. The construction was very precise, the base is aligned within 4 min of arc to the cardinal compass points using true not magnetic north, and there is only a 58mm difference in side length and 0.5 mm gaps between casing stones. This level of accuracy however was entirely within the mathematical and technical capacity of the time. They are surrounded by structures common to most funerary complexes such as a mortuary temple, boat pits, causeways and housing for guards and workers. The most unusual thing at Giza is the Sphinx and even that I think was just Khafre making use of a large chunk of sandstone that he otherwise would have had to clear. There are no schools, laboratories, libraries, or anything else you would consider scientific or academic in the area.

One final tidbit. The name Pyramid may have been given to them by Greek tourists, in Egyptian they were referred to as mer. The greeks have a type of honey cake that is pyramid shaped called a Pyramis. Its unclear which was named after which.