Modeling the Variability of Ancient Imperial Frontiers
Cross-culturally, empires proclaimed the notion that their territorial expansion was morally just and therefore had no limits (Drummond and Nelson 1994; Elton 1996; Turner 1993). Despite this ideological justification, their growth was not unlimited and often ended when marked economic, political, or ecological constraints were reached (Lattimore 1940; Whittaker 1994). Ancient empires usually expanded over continuous stretches of land, although their growth could be discontinuous and in the form of strategic advance nodes (Mackendrick 1965; Murty 1978; Parker 1998, 2002). Considering that territorial expansion often entailed subjugation by force, frontier regions were the setting of multifaceted socioeconomic processes. As discussed, some of these processes included marked military control and violence, surplus extraction of valuable local resources, village abandonment, depopulation, and rebellion. Depending on more favorable conditions, frontier regions could also become a venue of strategic economic development through thriving exchange networks and indigenous elite alliances, along with emulation and ethnogenesis.
Therefore, the variation in the magnitude and direction of these processes contributed to the formation of different kinds of imperial frontiers. On the one hand, approaches to explaining the nature of imperial frontiers have often viewed them as preclusive lines. Associated notions encompass constructs like hardened perimeters, barricades, and borderlines (Elton 1996; Lattimore 1940, 1962; Luttwak 1976; Parker 1998; Whittaker 1994). On the other hand, other scholars prefer to see ancient imperial frontiers as broader zones of interaction. Concepts like borderlands explain the fluid nature of frontiers as broad spaces of social interaction and as formed by overlapping boundaries and socioeconomic zones (Elton 1996; Lattimore 1940, 1988; Parker 1998; Whittaker 1994).
In reality, closed and open frontiers represent only two extremes of a broader continuum of possibilities. On one extreme is the closed, static, and preclusive linear frontier. On the other extreme is the open, fluid, and encompassing frontier zone (Anderson 1996; Martinez 1994; Parker 2002). Depending on the dominant socioeconomic processes, or degrees of frontier permeability, other intermediate variations are possible (Anderson 1996; Martinez 1994; Parker 2002).