No one knows the answer to this question, although there have been many guesses from expert archeologists. One of the most interesting things that I have seen is that they believe that the outside of the Sphinx was weathered by water for many years. This is pretty impossible in what is now the Sahara Desert; however, it may have been possible if the Sphinx is a lot older than has been thought previously, and was possibly either under water, or in an area that flooded a lot. Another interesting speculation is about the choice of a lion's body for the Sphinx, and they believe that it could represent that the astrological age of Leo was coming into being (like we are now in the age of Aquarius). The Sphinx faces exactly towards where the constellation Leo would have been seen in the sky at the time , making the connection even more likely.