In 1938, W. Benjamin elaborated a model of his major work, the Arcades Project, conceived as a social history of the city of Paris in the 19th century; the model remained unconcluded, but there is an integral plan of its construction, discovered in 1981 at the Bibliothèque Nationale of France. Based upon the deciphering of these manuscripts, 80% unpublished, this article presents a synthesis of the Arcades Model, in form of a constellation of the 30 colored sigla which symbolize the 30 constructive categories. The working hypothesis is that they are an esoteric script, with specific aesthetic, semantic and structurizing values: a mimetic instrument appropriated to read the enigmatic text of the modern metropolis. Seven aspects of the sigla are presented in this analysis: historiographical workshop, physiognomical scripts, visualization of time, history as cartography, pictures of mentality, allegorization, and history as radiography. As they operate on the boundary of conceptual and pictographical traditions, the sigla constitute a frontier genre in historiography.
