The southern façade of the Khafre Pyramid exhibits structural and lithotechnical anomalies that diverge fundamentally from the construction methods attributed to the Fourth Dynasty. Among these, the presence of a perfectly fitted red granite block embedded within the first limestone course is the most striking element. This block displays highly uniform pecking, a precision-engineered fit, and a complete absence of mortar, wedges or binding agents-features wholly inconsistent with known pharaonic masonry practices. The geological characteristics of the underlying Mokattam Formation reveal differential compaction, fracture systems, and stratigraphic discontinuities that would have required advanced knowledge of load distribution and mechanical stabilization. Engineering analysis shows that the granite block functions as a compression key, an architectural device designed to stabilise a heterogeneous substrate under extreme vertical load. Such solutions have no precedent in dynastic Egypt but appear in megalithic constructions of the Late Pleistocene and Early Holocene across several regions of the world. This study proposes that the southern base of the Khafre Pyramid belongs to a far older construction phase and that the pyramid itself was erected upon a pre-existing megalithic platform displaying sophisticated structural engineering. The archaeological and historical implications call for a reevaluation of the origin and development of the Giza Plateau.