From Pythagoras to the present day, via the exaltation of the astonishing virtues of the Golden Section, theorized by Luca Pacioli (1509), and later by Le Corbusier with Le Modulor (1949), in this book the author sets out to present and explore themes and theories of art (and architecture in particular) that refer in various ways to mystical-esoteric beliefs, or are based on the supposed superiority of Number in the analysis of artistic works. In many of these theories the author identifies attempts to subordinate artistic and architectural creation to the intervention of a Supreme Being, a Great Orderer who would create nature, following strictly mathematical principles. While there is no shortage of texts generally devoted to already well-known theories of architecture (the bibliography is vast), here the author considers various lesser-known esoteric and numerological theories, in which he attempts to identify some lines of continuity (or rupture). Through a tight critique he arrives at their demythicization, both relying, as much as possible, on principles pertaining to the sphere of rationality and starting from the material problems connected with the experience of building.