800 years of pyramids
But there are plenty of theories. The pyramids may have been a king's way of impressing the gods, his way of assuring himself a position as close to the divine world of the eternal world cycle. Also, the pyramid was at first though to give ultimate protection for the content of the tomb against grave robbers.
The shape is generally believed to reflect the 4 corners, or directions of the world: Where the sun rises (east), its highest point (south), where it sets (west) and the point where the sun reaches its lowest point (the opposite of south; north). The summit of the pyramid is the unity of the 4 corners.
As for the construction, it is really only the pyramids that are built from huge blocks, that have been entangled in mystery. Many pyramids are built from mud-brick or unimpressively small stones.
Some theories explain the moving of the huge blocks to the assistance of extra-terrestrial powers. But the most popular theories are more sober, explaining that ramps were built to allow large crews of workers to pull the stones from the ground up to their final position.
The true pyramid era lasted much shorter than most people believe. It started with the step pyramid of Zoser at Saqqara (which by definition isn't really a pyramid) around 2650 BCE and it ends around 1800 BCE. Pyramids built after this were mere reproductions and very small in comparison.
Snefru's 3 pyramids represent the best introduction to the challenges that faced the first pyramid builders. His Bent Pyramid is believed to have received its shape after the builders discovered that the walls rose too steep.
The largest pyramids rise higher than 140 metres above ground, but most are (or were, as many have fallen in) around 50 metres high. They all have inner corridors, and had outside temple complexes.
While the pyramid was built as the tomb of the king, it would soon develop into the centre of tombs of the rich. Large and small tombs were built as close to the pyramid as the owner or his family could afford.
Today there are 3 pyramid areas every visitor to Egypt should visit. It is of course Giza (which should be visited last of the 3, as it is the youngest but most impressive) and Saqqara. The third is Dahshur, which is best visited after you have spent a few hours around the complex of Zoser at Saqqara.
2) Entry is possible by crossing the desert from the main parts of Saqqara.