Despite the large volume of published work on Offa's Dyke there is no settled conclusion as to its original purpose. Many different and often conflicting theories exist, most of which can be put into three broad categories: defensive, political and economic. It is generally accepted that the monument's disposition relative to the adjacent topography is significant for interpretations of purpose. In this article, field survey and GIS mapping techniques are applied with respect to the comparative

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... size and topographical disposition of a stretch of central Offa's Dyke in order to examine its utility as a defensive structure. This allows a re-evaluation of claims by Hill and Worthington (2003), among others, that the route of Offa's Dyke was designed to optimise outlook by following the west facing brow of hills, or more generally to 'command' the western landscape. Evidence reported here shows that central Offa's Dyke does not consistently prioritise western views. Instead, it was positioned in such a way as to often obscure westerly vistas, despite the opportunity to optimise such an outlook by relatively minor route adjustments. On the basis of the evidence reported, discussed in the context of the wider literature, it is concluded that central Offa's Dyke should be interpreted as a physical obstacle rather than a defensive fortification. After a brief consideration of alternative theories of purpose it is suggested that Offa's Dyke was most likely built with economic and political, rather than defensive, functions in mind. It is postulated that control of trade provides a plausible context for its construction.