<P> Urban infrastructure involves various physical networks and spaces necessary for transportation, water use, energy, recreation, and public functions . Infrastructure carries a high initial cost in fixed capital (pipes, wires, plants, vehicles, etc .) but lower marginal costs and thus positive economies of scale . Because of the higher barriers to entry, these networks have been classified as natural monopolies, meaning that economic logic favors control of each network by a single organization, public or private . </P> <P> Infrastructure in general (if not every infrastructure project) plays a vital role in a city's capacity for economic activity and expansion, underpinning the very survival of the city's inhabitants, as well as technological, commercial, industrial, and social activities . Structurally, many infrastructure systems take the form of networks with redundant links and multiple pathways, so that the system as a whole continue to operate even if parts of it fail . The particulars of a city's infrastructure systems have historical path dependence because new development must build from what exists already . </P> <P> Megaprojects such as the construction of airports, power plants, and railways require large upfront investments and thus tend to require funding from national government or the private sector . Privatization may also extend to all levels of infrastructure construction and maintenance . </P> <P> Urban infrastructure ideally serves all residents equally but in practice may prove uneven--with, in some cities, clear first - class and second - class alternatives . </P>

Which of the following is not one of the five main principles of ancient greek city planning