This revealing text describes the exciting discovery and deciphering of the 5,000-year-old stone chambers and standing stones of pre-Celtic Ireland. At midwinter sunrise, Martin Brennan and his research partner observed a beam of light shining into the central chamber at Newgrange, illuminating a series of glyphs on the back wall. They went on to observe significant solar and lunar events at other chambers and stone complexes in the Boyne Valley and Loughcrew Mountains. Through a combination of careful observation, analysis of the astronomical alignment of the sites, and personal insight into the meanings of megalithic symbols and carvings, Brennan demonstrates conclusively that the passage mounds and chambers are actually sophisticated calendar devices, and that the abstract wheels, spirals, zigzags, and wavy lines are symbols of solar and lunar timekeeping.