The thing which first interested me in the subject of Archaeo-astronomy was the work of Robert Bauval and Graham Hancock on the Great Pyramid at Giza.
There are a number of mysteries about the Great Pyramid. Firstly as is widely accepted Egyptian pyramids are burial chambers for the Pharaohs, and in all cases there are Hieroglyphics and paintings covering the walls. If the Great Pyramid, the largest, most accurately built one of all was a shrine to the ruler why are there no hieroglyphics.
The ground breaking work on this came when the constellation Orion was studied. Orion was very important to the Egyptians as the constellation depicted the god Osiris, and the constellation was next to the celestial river (the close packed stars of the Milky Way).
Above on the left we see an image of the constellation Orion with just the major stars showing. Note closely the three diagonal ones at the centre of the image, Orion's belt, and on the right is the same constellation but with many more stars showing. Note the close packed stars of the Milky Way.
What Bauval realised was that the milky way was the river Nile in the sky and that the Giza Pyramids represented the stars of Orions belt.
The first image we see above is a close up of the second picture of Orion, zoomed in on the belt stars and the second is an overhead of the Giza pyramids. The things to note, which clinched it for Bauval, are firstly that they do not form an exact diagonal line, there is a slight offset in both pictures, and secondly that the pyramids are different sizes, which appear to correlate to the relevant brightness of the 3 stars
However these alignments indicate that it is much older than previously thought. Due to precession the constellation slowly moves it's relative position in the sky. Using modern computer programmes we find that the alignment matches in prehistory at a time when the sphinx would have faced Leo (the lion), a more natural association than the current Taurus (the bull). Also shafts in the Great Pyramid would point exactly to stars in the constellation at that time as shown in the graphic on the left. One alignment might be a coincidence, but another shaft would point exactly at Sirius another important star in myth and Legend.
Also the Sphinx shows signs of water erosion which indicates it comes from a much earlier time when the area was not desert.
It is also noticeable that the head of the Sphinx is much smaller than the body giving rise to the theory that it originally had the head of a lion as well but that a Pharoah had it recarved to his likeness at a later date. Alternatively, another researcher has said that the body does not have the tufted tail or large rear haunches typical of both real lions and those depicted in Egyptian art and puts forward that it is more like a dogs body or more probably the God Anubis.
Pyramids are found all over the world so was there a very ancient civilisation of world proportions.