You mean city planning? Rome wasn't planned. Livy complained that Rome's structure and planning was disgraceful, and that the city wound in whatever absurd directions it felt like. Rome had narrow, winding alleyways connecting areas of habitation, which packed as many people into as small an area as was possible. Even well into the Principate the seasonal Tiber flooding, which was not totally resolved until the Tiber was embanked in the nineteenth century, destroyed or rendered temporarily uninhabitable large stretches of the city's lowlands, and periodic catastrophic fires destroyed major chunks of the city. As such the city's landscape was always changing, as things were destroyed, rebuilt, built someplace else, added onto, etc. Moreover, trite as the saying is, Rome wasn't built in a day. The city grew from humble clusters of pastoral settlement on the Palatine and Esquiline into a truly unified city by the fairly early Republic, and eventually into the largest city in the western world before the modern period. Settlement expanded in a haphazard, generally unplanned way, responding sometimes to environmental changes like the establishment of the Emporium south of the Aventine or the expansion of the Forum under Caesar and Augustus, but also simply trying to fit people into available space. Buildings were demolished to make way for new constructions--Augustus prided himself on buying the property in the way of his forum rather than confiscating it--or were just attached to adjacent buildings.

In this respect Rome differed quite drastically from the neat, organized colonial foundations of the provinces and Italy. These cities, often founded on the basis of military camps, tended to have orderly, pre-planned, gridded streets. But their sites were also generally specifically selected (or founded on top of older settlements) and were begun from scratch with the intention of becoming cities of a certain size. Rome had no such forethought to guide it, and the early city simply grew organically. In certain respects the city's growth was affected by real geographical limitations that prevented the establishment of an orderly grid system. The hills of Rome cut Rome up into lowland corridors and highland districts, with the Tiber separating the majority of the city from the less densely populated Janiculum. Roads leading into the city from Italy converged, in the Principate, at Augustus' Golden Milestone, but habitation and construction often naturally followed these roads out at a considerable distance, notably along the Via Appia to the south. There appears to be little evidence for "districting" in Rome. Augustus' attempt to rationalize the administration of the city divided it up into Regiones and established clear models of administration and organization in the city's vici, or neighborhoods, which officially became the lowest level of urban administration. But Augustus could not reorganize the city, only make sense of what was there. While certain areas were sometimes over-representative of certain groups--the Palatine's position overlooking the forum, for example, drove property values up--the city generally shows few signs of ethnic, cultural, or socio-economic regionalization. We have a few references to what might initially seem like districts, but the evidence is poor. Juvenal and other writers disparaged the Subura and the Argiletum as seedy areas, but the presence of ancient aristocratic domiciles there shows that they were more likely areas of mixed habitation than what we might think of when we think of urban ghettos. Varro mentions a vicus Africus on the Esquiline, where supposedly Punic hostages had been settled after the Punic Wars, but it seems unlikely that it constituted a "Punic" district or that it maintained any ethnic character much past its initial settlement. This seems to make sense. Apart from the tendencies of Roman, and especially Republican, society, in which the senatorial class and equites were expected to interact constantly with their social inferiors as a matter of pride, fairly distributed patterns of residence would be well in keeping with what we know about the general population of Rome, which Ian Harrison described as "fluid." Death to disease alone outweighed births by even the freest estimates, and yet the city grew over time dramatically. People must have been coming into the city constantly, and within the city they (the majority of them being unskilled laborers) seem to have migrated throughout the city chasing work. There's a great deal more work to do on settlement patterns in the city (and the archaeology to support the textual evidence is lacking) but there seem to be good reasons for the rather dispersed picture of settlement in the city that we appear to see.

Where there was a certain amount of urban planning was the monumental building projects. The construction of fora, new temple complexes, and public buildings of various kinds necessarily required a certain amount of forethought. But even this was fairly haphazard. Magistrates built buildings when they could or when they wanted to, on whatever land was available, sometimes tearing down stuff in the way. Naturally most monumental construction took place on the Capitoline, in the Forum, in the Campus Martius, and in other large public spaces. But even then fitting new constructions in was not generally done according to rationalizing modern theories of urban design. The Basilica Porcia in the Forum was apparently built on top of shops and domus that were in the way. The Basilica Sempronia was built on top of the house of Scipio, Sempronius Gracchus' father-in-law, and itself was later demolished to make room for the Basilica Julia.