How did the Egyptians build the pyramids?

The pyramids of Egypt, dating back to centuries have stood the test of time. These huge structures were built of limestone and granite. Blocks of stone weighing up to 15 tonnes were used. It is said that about a lakh of slaves laboured for 20 years to build the Great Pyramid that houses the mummy of Pharaoh Khufu. However, they worked only for three months in a year, when the Nile flooded its banks. Then the granite would be brought from Aswan, floated downstream to a specially built jetty at the site of the pyramid. The stones would then be dragged up big, long, sloping ramps and fitted into place.