We can assume with relative certainty that after the 1218 fire the clergy invited a procession of artisans to visit the site and propose a program to fix the cathedral--perhaps the old structure could be repaired, or an entirely new one conceived.  The key evidence attesting to this kind of architectural competition comes from the account of the rebuilding of the chevet of Canterbury Cathedral (Tractatus de Combustione) after the 1174 fire written by the former sacristan, Gervase of Canterbury.  At Canterbury the final choice, according to the chronicler, depended upon three things: the ability of the artisan to find the right language to talk with the clergy who were in a state of shock after the disastrous fire, his logistical ability to marshal supplies of stone and organize the process of planning and construction, and, third, his "lively genius."  That genius would involve the ability to project an image of the total edifice as something that could be grasped, internalized, and held in the head for as long as it took to achieve completion.  At Amiens that image involved a dynamic geometric scheme that unfolded from a great central square, giving the overall dimensions of nave, transept and choir.  The application of square schematism expanded into double and triple squares lent coherence to plan and elevation.  Perhaps Robert of Luzarches employed graphic means (small-scale drawings) to project these mechanisms in his early meetings with the clergy.