Workers gradually carved the 240-foot long and 66-foot high Sphinx statue from a massive piece of limestone, according to Smithsonian Magazine. These measurements make the Sphinx one of the largest monolithic statues in the world.
Ancient Egyptian workers cut the Sphinx statue from the lowest layers of the Mokkatam Formation, according to the Ancient Egypt Research Association or Aera. These layers sat directly on top of the much harder petrified reef, giving the statue a solid foundation. The layers of the sphinx itself are quarried limestone blocks, which were formed over millions of years from petrified mud. Aera also explains that, although the Sphinx is a solid piece of stone, it was carved in naturally occurring layers. The head and neck were carved from much softer rock, which explains why such features as the nose have seen greater effects of erosion than the rest of the statue, which was carved from much denser stone.
Although these theories are widely held to explain the carving of the Sphinx, there are other alternative theories about the statue's formation. Some groups believe in the water erosion hypothesis, according to Wikipedia. This hypothesis states that the Sphinx was formed as significant rainfall gradually caused extensive erosion of the rock and that created the rough shape of the statue.