The study of the Roman frontier is the oldest of archaeological subjects, much of the initial work being done by German scholars around the beginning of the nineteen hundreds. For this reason we know a startling amount about the physical remains in areas such as the Rhine and Danube. Parts of the frontier have also become sites of historical importance for the whole world such as Hadrian’s Wall and its Antonine counterpart.
Sites such as these can be found throughout the roman empire and link together to form what is known as Limites, the best known being the Limes Germanicus, Raetia, Britannicus, Moesiae, Tripolitanus and Arabicus. These are portions of the Roman frontier that show systematic fortification and military presence. The request that was asked of this blog specified that the frontiers’ fortifications where of particular interest. While it sounds relatively simple to write a short piece on the general history of fortifications and their evolution in these regions. This would not be able to convey the sheer diversity that the frontiers exhibit (and is really not interesting). To understand the reason for this variation we must look at the key factors in a frontiers existence (in other words, “what I really want to write about”).
First a frontier is primarily defined via those who place and maintain it and those whom it was used against. To understand each part of the frontier system of the Roman Empire, those on the far side of the border must be understood as well. How they acted and interacted with the Roman people influenced the construction and placement of the frontiers as well as the numbers of troops garrisoned there at any one time. An example of this is best shown in the Limes Tripolitanus. This frontier system crossed most of modern day North Africa. The construction of the frontier appears to have taken into account the needs of the natives and those tribes living further south. The frontier itself is placed just south of the best agricultural land in the region thereby securing it for the Roman provinces. But it was not a closed frontier composed of a solid wooden palisade. Instead the frontier was open, to allow the natives across the frontier (who consisted mainly of nomadic tribes of herdsmen), to travel into to the province to trade with the provincials. Here it is possible to see that the frontier was to some degree designed to suit the needs of provinces it straddled. The result of this to the bigger picture of the empire is this, if a frontier is suited to deal with those natives that lie across from it then due to the mass variation of the neighbouring tribes and civilisations that could be found next to or near the empire, then the frontier and its fortifications must exhibit variation to account for this.
The second reason for such diversity in an apparently uniform subject is the sheer geographical variety of the Roman Empire (The actual second reason for such diversity in an apparently uniform subject is that it gives academics a lot more to write about). Each province provided the Roman military a unique and challenging location to establish a frontier. This included most forms of geographical landscape form the great rivers of central Europe to great deserts regions of Northern Africa. The challenge of managing mountainous regions also had to be overcome in areas such as the Alps and the Carpathians. Each of these geographical forms presented challenges of their own. The deserts focused much human activity on water management and therefore most human settlement and trading routes where placed between several sources of water. Here the Roman military had to create a frontier that concentrated on controlling these key points in the landscape. While in mountainous regions human interaction was often confined to key passages through mountain ranges. Rivers presented a very unique problem, they were predominantly used to aid communication and movement (as any Egyptologist will tell you) but in the case of rivers such as the Rhine and the Danube this was balanced by the dangerous power that such large rivers can bring to bear. The geography of each provinces location was an important factor in the creation of frontiers. The actual construction of these frontiers was also affected. The Roman military was often extremely practical when it came to building materials. Often the most available and easily created materials where used (in other words timber). The timber made fortifications often common under the Early Emperors (During the republican period long term fortifications were extremely uncommon) were eventually replaced under later rulers with more robust stone. This marked a more static life for the military and a more defensive role in their actions. But again stone was chosen for its relative abundance in areas such as central Europe. In places such as Northern Africa and the Near East early forts were made out of mud brick and would eventually be replaced by sand stone. In each case of each of these locations the frontier was not only shaped by the landscape but also by the construction material available.
Finally (I hope you’re still with me) the borders of the Roman Empire differed as because they were built at different times and under the instruction of different people (The old “too many cooks vary the frontier” syndrome). Most frontiers where built under different emperors. On top of this those who actually built and maintained the frontier where the provincial governors (It is unknown how much influence the position of emperor had over the day to day maintenance of the frontiers). At any one time during the imperial period the German limes were under the control of at least two provincial governors (Germania Supperior and Inferior). In this way it is unlikely that there was ever a single organised effort to protect the borders of the empire. Instead a rather more erratic and random collection of building and renovation programs were undertaken by a large and ever changing collection of individuals who may or may not have cooperated with each other. A good example of this is the differences between the two emperors Trajan and Hadrian. Trajan is often shown as an expansionistic emperor, with significant additions to the empire in the east. His successor Hadrian has been depicted as a more pragmatic individual who attempted to secure those portions of the empire which could be reasonably defended while retreating from those gains which were more problematic. If there was such difference in foreign and defensive “policy” between successive emperors then there is little chance that the frontiers built during their reigns could be reliably thought of as similar.
Therefore I now hope that you can understand the sheer mass of variables that must be taken account of when we talk about frontiers. I do realise that around about now you are becoming aware that I haven’t actually dealt with any real information on frontiers or borders. This can be taken two ways, one if you are interested in this and wish to know more please let us know and I will happily continue some form of series of posts on frontiers. Second and most importantly if you want a straight answer don’t ask an academic.