In a well-known passage, the Greek historian Polybius, writing in the mid-second century BC, attributes Rome's success as a republic to a perfect balance of power between its constituent elements, army, senate and people (Histories 6.11); and indeed, the Republic's long survival was an achievement worth explaining. On another note, over a century later, Livy remarked how Republican Rome, with its rambling street plan and miscellany of buildings, compared unfavourably with the magnificent royal cities of the eastern Mediterranean; he put this down to hasty rebuilding after a great Gallic conflagration around 390 BC. Few scholars now accept his explanation. A handful of scholars argue for underlying rationales, usually when setting up the early city as a foil for its transformation under Augustus and subsequent emperors, and their conclusions tend towards characterizing the city's design as an unintended corollary to the annual turnover of magistrates. This article, likewise, argues for the role of government in the city's appearance; but it contends that the state of Republican urbanism was deliberate. A response, of sorts, to both ancient authors' observations, it addresses how provisions to ensure equilibrium in one of the Republic's components, the senatorial class, in the interests of preserving the res publica, came at a vital cost to the city's architectural evolution. These provisions took the form of intentional constraints (on time and money), to prevent élite Romans from building like, and thus presenting themselves as, Mediterranean monarchs. Painting with a broad chronological stroke, it traces the tension between the Roman Republic in its ideal state and the physical city, exploring the strategies élite Romans developed to work within the constraints. Only when unforeseen factors weakened the state's power to self-regulate could the built city flourish and, in doing so, further diminish the state. Many of these factors — such as increased wealth in the second century and the first-century preponderance of special commands — are known; to these, this article argues, should be added the development of concrete.