"Planning a city with a street pattern that is based on a system of vertical co-ordinations has been common practice accross centuries and cultures in urban history. Being a persistent phenomenon, the urban grid has often attracted the attention of scholars; its origin and its various "metamorphoses" (formal variety) adopted by different culturies and societies are issues raised in common by a number of studies. "Griddy" cities are usually discussed in detail from the point of view of form; overall shape, subdivision in blocks, axial and symbolic properties of the street pattern, e.t.c. Their public open space is usually analysed by means of geometry, often compared to public open space in cities without grid. Geometrical regularity is somehow juxtaposed to geometrical irregularity. There seems to be a trend in litterature to either classify together all "griddy" urban settlements because of the existence of the grid itself and as opposed to settlements with deformed street pattern or, distinguish purely formal types among them. In Classical Antiquity for instance, the Greek "poleis" with grid-patterned street system are considered one type of urban space as opposed to the type of the "old" Greek cities with irregular street system. The grid of the Roman "civitas" of the Imperial Age is seen as a distinct metamorphoses of the Hippodamian grid of the Greek poleis - a metamorhoses which involves only formal differences dictated by reasons of different culture, architectural style and tradition. Such formal classifications of the urban grid imply the belief that urban grid has no other structure appart from its formal structure; it does not exhibit spatial order and hierarchy, as opposed to urban settlements with "deformed" street patterns that generate deep structure of space. This paper develops the argument that the urban grid is not deprived of internal spatial structure. For this purpose, a number of "griddy" cities of Classical Antiquity, both Greek and Roman, are studied from the point of view of space. Two main questions are raised: Do formal differences between the Greek and the Roman urban grid imply distinct internal structure in terms of space? What are the spatial types of square (Agora and Forum) generated by these two urban grids? The analysis uses the theory and the methodology of Space Syntax as developed by Prof. Bill Hillier, University College London."