The Giza Pyramids, built to endure an eternity, have done just that. The monumental tombs are relics of Egypt's Old Kingdom era and were constructed some 4,500 years ago. Egypt's pharaohs expected to become gods in the afterlife. To prepare for the next world they erected temples to the gods and massive pyramid tombs for themselves—filled with all the things each ruler would need to guide and sustain himself in the next world. Pharaoh Khufu began the first Giza pyramid project, circa 2550 B.C. His Great Pyramid is the largest in Giza and towers some 481 feet (147 meters) above the plateau. Its estimated 2.3 million stone blocks each weigh an average of 2.5 to 15 tons. Khufu's son, Pharaoh Khafre, built the second pyramid at Giza, circa 2520 B.C. His necropolis also included the Sphinx, a mysterious limestone monument with the body of a lion and a pharaoh's head. The Sphinx may stand sentinel for the pharaoh's entire tomb complex. The third of the Giza Pyramids is considerably smaller than the first two. Built by Pharaoh Menkaure circa 2490 B.C., it featured a much more complex mortuary temple. TODAY’S POPULAR STORIES SCIENCE & INNOVATIONSTARSTRUCK Bizarre comet from another star system just spotted SCIENCE & INNOVATION Water found on a potentially life-friendly alien planet ANIMALS Centuries of breeding have reshaped dog brains—here’s how Each massive pyramid is but one part of a larger complex, including a palace, temples, solar boat pits, and other features. Building Boom The ancient engineering feats at Giza were so impressive that even today scientists can't be sure how the pyramids were built. Yet they have learned much about the people who built them and the political power necessary to make it happen. The builders were skilled, well-fed Egyptian workers who lived in a nearby temporary city. Archaeological digs on the fascinating site have revealed a highly organized community, rich with resources, that must have been backed by strong central authority. It's likely that communities across Egypt contributed workers, as well as food and other essentials, for what became in some ways a national project to display the wealth and control of the ancient pharaohs.