Network Analysis of Transport Vectors in Roman Baetica
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Network Analysis of Transport Vectors in Roman Baetica Leif Isaksen Department of Archaeology University of Southampton Great Britain [email protected] Abstract The Roman province of Baetica, roughly commensurate with modern Andalusia, Spain, provides an excellent case study of “Romanization” from its early days as a republican overseas possession to its development into a pillar of the imperial economy. The work presented here uses Network Analysis applied to our current knowledge of transport and communication routes in the region in order to better under- stand the relationship between the location and political/economic significance of sites. This paper focuses on the technological aspects of the study, in particular the methodology used, as well as the results, which indicate strong transport-influenced spatial patterning. The concluding section takes a deeper look at the nature of the source data and its “directionality.” 1 The Project This paper is based on a master’s dissertation at the University and a wealth of data there is still a lot that is uncertain. This of Southampton, Great Britain (Isaksen 2005) and comple- paper will contend that the branch of economics known as ments a paper in preparation for the proceedings of the CAA Transport Geography may be able to contribute a great deal, UK Chapter (Isaksen In Press). The research itself has been particularly in its use of Node Networks, an abstract model undertaken in conjunction with Urban Connectivity in Iron of the interactions between spatially separate locations. Age and Roman Southern Spain, an Arts and Humanities Research Council funded project based at Southampton University that aims to “analyze changing social, economic 2 The Lie of the Land and geographical relationships between towns and nucleated settlements in southern Spain…between c.500 BC and AD Baetica, a province created from the southerly part of 500” (Southampton University 2003). The principle theme Hispania Ulterior by Augustus in the late first century BC, of the research is to explore and develop methodologies by is roughly commensurate with modern Andalusia (Figure which to understand the network of relationships that existed 1). Its primary importance to Rome, and indeed many of between nucleated settlements in the region. The scope of its previous inhabitants, was the valley of the River Baetis the project is limited to the province of Seville, once the (Guadalquivir) with its broad plains and fertile soil, and economic hub of Baetica, and it is to this framework that the the Mons Marianus (Sierra Morena) mountain range to its work below contributes, though the area considered has of neces- sity been extended in order to better understand some of the influences on the network. In many ways the Roman province of Baetica is an ideal subject for exploring new approaches to historic transport geography. Perhaps surprisingly, this is not due to the complete- ness of its record (for it is not), but because it provides a remark- able breadth of pertinent data (Sillières 1990:9-16). It is only by approaching this variegate jig- saw from a range of angles that a picture begins to emerge. This has been done fairly recently in two major works, Sillières (1990) and Corzo-Sanchez and San Gil (1992), but despite much well-reasoned argument Figure 1. The Province of Baetica with district boundaries, capitals and principal watercourses. 64 north, rich in precious metals. The regional economy was a specific stretch of the river, and the rest of the territory not merely dictated by its resources, however—it was also divided approximately equally around these central axes. Of greatly affected by its topography. The central valley is vir- key importance, of course, is the main channel of the Baetis, tually cut off to the north, south, and east by two significant which links the key towns of Corduba and Hispalis and pro- mountain ranges, the Sierra Morena and the Cordillera Sub- vides access to the sea. Of lesser but still notable signifi- Bética. The natural entry and exit point was therefore via the cance is the Singilis (Genil), a tributary of the Guadalquivir large tidal estuary (the lacus ligustinus) to the West, which that is navigable as far as the colony of Astigi and which was exposed not to the Mediterranean but the Atlantic. The bisects much of the fertile plain. River Baetis (Guadalquivir) itself is navigable some 200 km inland and the colony of Corduba (Cordoba), capital of Hispania Ulterior and later Baetica, was founded at its fur- 3 The Mystery thest navigable point. To complement this natural conduit, the province devel- One way of approaching landscape geography is to start with oped a complex network of roads. These are testified to by “coincidences” and a look at the map shows a coincidence numerous milestones and a number of bridges throughout that seems unusual. Despite the fact that the larger expanses the region. They not only linked towns within the interior, of agricultural land are all south of the Guadalquivir, virtu- but also connected them to neighboring provinces, often ally all the towns on the lower Guadalquivir lie along its providing guidance and sure footing through tortuous moun- right (northern) bank. Of those mentioned by Pliny and tain valleys. On a more regional level, they would also have Strabo, the towns of Caura, Osset, Italica, Ilipa Magna, been necessary to enable wheeled vehicles to transport local Naeva, Canania, Arva, Axati, and Celti have been identified produce to local markets or entrepôts from whence it could with locations to the north/west whereas only Orippo and be shipped to the wider empire. Hispalis are to the south/east. This observation leads to the It is not an understatement, however, to say that the assumption that something other than agriculture was either River Baetis, after which the province was named (Pliny, attracting towns to the north bank or was discouraging them NH, 4.4), is the single most important factor in understand- from occupying the south bank, or both. ing the transport geography of Baetica. To quote another A study of the elevation of the region hints at the reason scholar, “it was the one outstanding geographic feature in for this occupation pattern. The sites are located not only at Baetica’s dynamic economic history” (Ponsich 1998:173) the points of maximum distance from the mean course, but .As just one indication of the river’s importance, three of also at points where the ground rises steeply away from the the province’s four jurisdictional capitals, Cordoba (also the river. Virtually all the towns are built close to, but above, the provincial capital), Hispalis, and Astigi lay at the ends of its river, a striking correlation which only begins to decrease as navigable branches. The fourth, Gades, had jurisdiction of we approach the ancient lacus. the coastal towns, relatively inaccessible from the interior, In fact, the cause is not a mystery and is well known but was also close to the mouth of its estuary. In fact, if we to current long-term residents of region. The watershed of return to what we know of the extents of the four Baetican the river is a huge region incorporating several mountain- conventus, based upon the location of towns within them, ous areas and, consequently, the river floods frequently and a clear pattern emerges (see Figure 1). The three northerly sometimes dramatically, especially downstream of its con- conventus are not divided east-west, but around the conflu- fluence with the Genil (Vanney 1970:89). Figure 2 shows ence of the Baetis and the Singilis. In other words, each the numerous floods since the 16th century, but the apparent capital’s authority seems to have been deliberately based on increase in frequency is liable to be an artifact of better pub- lic record-keeping than due to a change in climate. A flood in the 12th century may have been responsible for as many as 63,000 deaths and there are no extant monuments in Seville from this period at less than 10 m above sea level. If the death toll is correct, it was the worst river flooding catas- trophe in recorded European history (Vanney 1970:111-2). It is likely, then, that the siting of the towns along the river is a response to this threat. The asymmetry between the left and right bank means that, to avoid the Figure 2. Flooding in Seville in meters above sea level since 1500. Much of the city lies at less than risk of flooding, those to the 10m above sea level (Vanney 1970:111). south must be situated at a 65 distance several kilometers from the main stream. Despite of available evidence is the Roman itineraries. Textual and the apparent disadvantages of the right bank, it provides a epigraphic evidence strongly suggests that guides for trav- series of low bluffs which remain above the floodwaters but, elers in the ancient world were based on topology rather crucially, give direct access to the water. Fresh water is not than topography. That is to say, almost every certifiable likely to be the principle reason for proximity to the river; “travel guide” we possess (pictorial or textual) indicates the with access to much cleaner sources from the faster flow- position of locations in relation to other ones, rather than ing mountain streams, and fishing as only part of a mixed embedding them within an independent spatial matrix, such economy, it can be concluded with a reasonable degree of as a Cartesian coordinate grid (Brodersen 2001:9-12). likelihood that direct access to the river itself, i.e., for trans- Most of our information comes in the form of various portation, is the determining factor.