The irregular pattern of Rome, clearly resulting from the lack of a master plan, is defined by Livy (V, 55, 5): forma … urbis … occupatae magis quam divisae similis. The regularity or irregularity of town forms depends entirely on the presence or absence of spontaneity in their birth and growth. The irregular city is the result of development left entirely to individuals who actually live on the land. If a governing body divides the land and disposes of it before it is handed over to the users, a uniformly patterned city will emerge. In accordance with this rather obvious determinant, Athens and Rome had to be irregular in pattern. The regular plan is found in Greek and Roman colonies and in cities that had been subjected to complete destruction and rebuilding. Most especially, uniformity is found in colonies where egalitarianism prevailed. Compare Roman and Greek colonies with those of the seventeenth and eighteenth centuries, formed on a rigid chessboard plan: Buenos Aires, Lima, Philadelphia, and so on.
Regular planning took form in the ancient cities chiefly by use of orthogonal subdivisions, as it did also in the colonial cities just mentioned and in certain medieval cities.1 It can also be seen in entirely different environments, among the Aztecs and at Peking even at the time of Marco Polo. More than from ritual values, the orthogonal system was employed because of its practicality and aesthetic appeal.2 There are no records in the ancient world of other regular forms such as the circular, star-shaped, and polygonal plans known in the Renaissance and Baroque eras, inspired by theories of the ideal city or of scenographic effects.
The orthogonal plan mirrors a principle widely known throughout the Orient and among the Minoans–Mycenaeans; the plan is so basic in nature that we need not look for any derivation. There seem to be no pathways for adopting Oriental styles, with the exception of some Egyptian influence. Diffusion of the orthogonal style cannot be attributed to the Phoenecians, for Soluntum and Selinus are Greek cities, not Punic.
The orthogonal system arose first from the right-angle intersection of two roads; it is found in the sixth-century Greek world no less than in the Etrusco–Italian settlements. Orthogonal plans are therefore not to be considered specific to Etrusco–Italian urbanism. The importance of this type of urbanism must be sharply limited when we exclude not only the terremare settlements but also Marzabotto, Capua, and Roma Quadrata and when we attribute the theories of the gromatici to the erudition of the late Republic.
On the other hand, the division by means of strigae, usually one actus wide, is interesting. It is documented in both the Greek and Etruscan cultures from the first half of the fifth century and must be allied to the work of Hippodamus of Miletus. This common urban style, expressed in both design and measurement, is one of the clearest expressions of the ties between Greece and Italy.
Although the Hippodamean plan is employed through the Hellenistic era, it is used in only a few cities by the Romans because in the fourth century B.C. the centralized plan began to be developed. Compared with the monotonous repetition of the plan as used in the Hellenistic world, the Romans achieved considerable variety in type of design and range of dimensions.
Uniform planning as developed in the ancient world included the theoretical study of climate and sociology. Theory preceded the practice of the planners and followed it as well. The studies that followed their work not only adhered to reality, as in Hippocrates, Aristotle, and Vitruvius, but also ventured into fantasy, creating ideal cities, as we see in Plato and Aristophanes, or refinements rooted in cosmic concepts, as in the Roman doctrine of delimitation.