Giza Necropolis

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, 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.[citation needed]

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 erroded as time has passed.[citation needed]