Architectonic size (proportions) has remained a fundamental, if optional, architectural concern throughout much of the course of modern architectural history. However, the same could not be said about ??urban size', understood as the one brought into existence by means of ??urban walls??, i.e. blocks. Indeed, today, cities across the world face serious problems of excessive growth, making it almost impossible to know when we are in or out of them; the limits of the city are nowhere to be seen. Thus the problem of the size of the city at large and more readily, that of the urban block, though not less active, has tended to remain not only overlooked but, more to the point, completely out of reach of current urban knowledge. From this point of view, it could rightly be asserted that the size of the block has become an urban intangible, so to speak. The overriding aim of this research is precisely to exhume from oblivion this silent but ever-active agent of urban reality by means of a critical analysis the size of the American block.