ancient cities

936 Urban System
and uncertainties. Early cities also were places
where the profits from selling agricultural surplus
were reinvested in other kinds of activities, leading
to innovations stimulated by the competition in
trade with other cities and giving rise to a more
and more complex social organization. Cities
exploit, then, not only a local site but a nodal
geographical situation and develop as long as
the networks they control are expanding.
Archaeologists have demonstrated that ancient
settlement systems possessed the same structural
properties as the urban systems observed later in
history or even today.
The earliest mention of urban system (“le système
général des villes”) is found in the article
“Villes” in a French encyclopedia; the article was
written by a Saint-Simonian engineer, Jean
Reynaud, who enunciated the main principles of
central place theory in 1841. But the classical formulation
of this theory belongs to German geographer
Walter Christaller. His thesis was inspired by
a general concern of the time about the role of
towns as marketplaces in rural regions. However,
in Christaller’s work, a systemic conception
remains implicit. Not until the 1960s was the multilevel
organization of urban systems first formalized
in systemic terms by American geographer
Brian Berry, who coined the famous phrase “cities
as systems within systems of cities.”
Central Place Systems
Central place theory intends to explain the size,
number, and spacing of cities. It defines centrality as
the property of cities to act as central places retailing
goods and services to surrounding areas (the
“complementary region” in Christaller’s words).
The theory includes behavioral hypotheses about
consumers, who try to minimize the travel costs for
acquiring goods and services, and suppliers, who
enter the market as long as they can make profit. A
postulate is that establishments supplying central
goods group, according to their own spatial ranges
and viability threshold, in centers of different sizes
and form six to seven hierarchical levels of central
places. Under these constraints, Christaller derives
three types of spatial models of urban hierarchies,
which optimize either the accessibility to markets
for consumers or the length of required transportation
networks and obey an administrative principle
of noncompetitiveness. Each of these spatial models
is characterized by a fixed ratio between the size
of market areas of two successive levels: This ratio is
K = 3 for the model following a market principle, 4
in the case of the transport principle, and 7 for the
administrative one.
The theory has been exemplified by many case
studies and tested in many regions of the world and
for various historical periods. Whereas the hierarchical
organization of retail functions was generally
observed, exhibiting a strong correlation with city
size, the regularity in K values was more difficult to
establish. Central place theory also was applied to
seasonal markets and to the spatial organization of
commercial activities inside cities. In this latter
case, however, the spatial regularities had to be
understood not within the framework of topographical
space but in reference to a time–space, as
defined by temporal measures of accessibility.
Central place theory was criticized from various
points of view. Inconsistencies in derivation of geometric
models were noticed, especially because the
local effects of population concentration are not
considered by Christaller as altering the hypothesis
of spatial homogeneity that is required for drawing
hexagons around each center. Lack of coincidence
with observations were also reported, namely, violations
of the hypothesis allocating consumers to
the nearest retail center for every purchase: At least
in highly mobile societies, consumers make multipurpose
travels that short-circuit the smallest shopping
centers and increase the contrasts in the
hierarchical organization. In parallel, an increase
in income trivializes previously rare services.
Moreover, it becomes less and less relevant to build
a theory of urban systems on the relationship
between cities and countryside, when three quarters
of the total population is urban. But the main
weakness is that central place theory is incomplete
for two reasons: (1) It does not consider other specialized
functions that cities are performing and
which do not serve a regional population (as manufacturing
activities or tourism), and (2) Christaller’s
theory is mainly a static one.
Urban Hierarchy as a
Statistical Distribution
A second type of interpretation of the hierarchical
differentiation in urban systems has followed a