The Great Pyramids were built at the direction of Pharaohs Khufu and Khafra in the 26th century BC. They are almost entirely solid rock and were built to hold the mummified corpses of kings in a small room filled with precious jewelry. Elaborate safeguards failed, and the pyramids were plundered of treasure not long after being completed. In the Middle Ages, it was widely and mistakenly believed that the Pyramids were spacious storehouses for emergency grain rations, and were built by the Biblical Hebrews (forerunners of today's Jews). In fact, the Pyramids predate the Hebraic period by several centuries, and the amount of open space inside consists of a tiny burial chamber, not sufficient for the purpose of being a granary.