Houdin's father was an architect who, in 1999, thought of a construction method that, it seemed to him, made more sense than any existing method proposed for building pyramids. To develop this hypothesis, Jean-Pierre Houdin, also an architect, gave up his job and set about drawing the first fully functional CAD architectural model of the Great Pyramid. His/their scheme involves using a regular external ramp to build the first 30% of the pyramid, with an "internal ramp" taking stones up beyond that height. The stones of the external ramp are re-cycled into the upper stories, thus explaining the otherwise puzzling lack of evidence for ramps.