Most construction theories are based on the idea that the pyramids were built by moving huge stones from a quarry and dragging and lifting them into place. The disagreements center on the method by which the stones were conveyed and placed and how possible the method was.
In building the pyramids, the architects might have developed their techniques over time. They would select a site on a relatively flat area of bedrock—not sand—which provided a stable foundation. After carefully surveying the site and laying down the first level of stones, they constructed the pyramids in horizontal levels, one on top of the other.
For the Great Pyramid of Giza, most of the stone for the interior seems to have been quarried immediately to the south of the construction site. The smooth exterior of the pyramid was made of a fine grade of white limestone that was quarried across the Nile. These exterior blocks had to be carefully cut, transported by river barge to Giza, and dragged up ramps to the construction site. Only a few exterior blocks remain in place at the bottom of the Great Pyramid. During the Middle Ages (5th century to 15th century), people may have taken the rest away for building projects in the city of Cairo.
To ensure that the pyramid remained symmetrical, the exterior casing stones all had to be equal in height and width. Workers might have marked all the blocks to indicate the angle of the pyramid wall and trimmed the surfaces carefully so that the blocks fit together. During construction, the outer surface of the stone was smooth limestone; excess stone has eroded as time has passed.
The pyramids of Giza and others are thought to have been constructed to house the remains of the deceased Pharaohs who ruled over Ancient Egypt. A portion of the Pharaoh's spirit called his ka was believed to remain with his corpse. Proper care of the remains was necessary in order for the "former Pharaoh to perform his new duties as king of the dead." It's theorized the pyramid not only served as a tomb for the Pharaoh, but also as a storage pit for various items he would need in the afterlife. "The people of Ancient Egypt believed that death on Earth was the start of a journey to the next world. The embalmed body of the King was entombed underneath or within the pyramid to protect it and allow his transformation and ascension to the afterlife."
The Giza pyramid complex at night
The sides of all three of the Giza pyramids were astronomically oriented to the north-south and east-west within a small fraction of a degree. Among recent attempts to explain such a clearly deliberate pattern are those of S. Haack, O. Neugebauer, K. Spence, D. Rawlins, K. Pickering, and J. Belmonte. The arrangement of the pyramids is a representation of the Orion constellation according to the disputed Orion correlation theory.