Research into the true costs of travel in archaeological societies has been largely ignored, particularly in pre-industrial, pre-state and prehistoric societies, where documentary sources that might enable us to calculate relative travel costs are absent. Additionally, while there is some analogical evidence for the relative cost of different forms of land transport, there is even less data available for calculating the cost of travel on water relative to that on land, apart from some figures for Roman industrial-scale transport. This situation desperately needs to be remedied, instead of uncritically relying on estimates derived from, for example, 20th-century small-scale foragers in sub-Saharan Africa, and applying these to a completely non-analogous society such as the Iron Age of Orkney.
I have shown that minor and easily implemented changes to a basic slope-based cost surface can yield radical changes in the 'least cost' pathways generated between two discrete sites. In particular, prioritising water transport in an island environment can substantially change the least-cost routes generated, particularly between coastal sites. In the case study of Iron Age Orkney, changes to the cost surface reflecting a desire to move about the landscape openly or invisibly similarly changed the calculated least-cost routes; however, the highly visible routes tended to coincide closely with those calculated solely on the basis of lowest energy cost, whereas the lowest-visibility routes diverged, sometimes radically, from the former two. While the precise implications of this are unclear without further analysis, they could suggest a desire either to make movement between sites as visible as possible, whether for the purposes of demonstration or defence. One avenue through which this could be clarified would be a closer questioning of what transportation technologies were available in the region during the Iron Age, with a goal of better understanding what the 'typical' avenue of approach to a broch site would be during this period.
An early version of this paper was presented at the 2005 CAA meeting in Tomar, Portugal. Since then, it has benefited from discussions with several people. The author would like to thank in particular Leif Isaksen and Dr David Wheatley (University of Southampton) and an anonymous reviewer for their comments and suggestions. The author is, of course, solely responsible for any errors or omissions remaining.
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