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Recent projects
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French Azilum: Crossroads of Revolutions
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The Upland Landscapes of Slievemore Mountain
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Enfield Falls Archaeological Research Project
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Dun Kilmore promontory fort, Achillbeg Island, Co. Mayo, Ireland

Achillbeg and Achill Island Promontory Forts
Dr. Johanna Ullrich
PhD Research
UCD School of Archaeology
Co. Mayo, Ireland


The Project

This study is the basis of my PhD thesis, and the research was undertaken to both prove the applicability of phosphate analysis to sites whose histories are not well understood and to allow for new interpretations of promontory forts.  Promontory forts are defined typologically as sites where a ditch and bank complex was constructed across the narrow isthmus of a natural headland.  This act of segregation formed a space surrounded on three sides by sea-cliffs and on one side by the complex itself (Macalister 1928: 286).  Promontory forts are found in Ireland, the Isle of Man, Scotland, Wales, Cornwall and Brittany.  They are present on a wide range of natural headlands and seem to display much variety in the form and use of the enclosed area.   Four promontory forts were selected for phosphate analysis to show how the technique can be applied to archaeological sites to interpret site-specific uses and reconstruct trends in community behavior on a site-type where other archaeological techniques have failed to determine their primary function. 

Distinct differences were visible in the phosphate patterning from the tested headlands.  Several of the tested promontory forts indicated they were used only for utilitarian purposes, such as look-out points and sea access, while others showed the presence of more symbolic uses as well. Although phosphate pattering on each of the promontory forts varied slightly, the patterns are comparable and formed homologous use-of-space models.  The placement of specific landscape components is different on each promontory fort, but the function of the components remains the same.  Distinct differences were also visible in the phosphate patterning from the tested headlands.  Several of the tested promontory forts indicated they were used only for utilitarian purposes, such as look-out points and sea access, while others showed the presence of more symbolic uses as well.   The constructed use-of-space models allowed these underlying similarities to become apparent in the role of promontory forts in the study area. Results from all tested sites identified two main areas of mid-level phosphate increases, with smaller-scale patterns linking the two areas of greater use. The two main areas of increased phosphate content on each fort are located on both the most exposed and the most protected areas of the forts.  This indicates use of the headlands as look-out points with associated basecamps.  Phosphate patterning also indicates an emphasis on the role of promontory forts as physical and cultural boundaries through the strict regulation of access to the forts, and for the advertisement of presence on the coastline.  

The application of phosphate analysis

 The archaeological examination of promontory forts in Ireland has thus far been limited to site surveys and a very small number of excavations (Barry 1977; Casey 1999; Liversage 1968; O’Kelly 1952; Sidebotham 1949). Initial periods of use of promontory forts and the original purpose of construction of the sites remain unclear (O’Kelly 1952: 38; Casey 1999: 62).  I used phosphate analysis techniques on several promontory forts to identify phosphate patterns and suggest possible uses of these sites.  The comparison of the phosphate patterns present on tested forts led to the construction of models for ancient uses-of-space on promontory forts. A greater understanding of the similarities and differences in how these sites were used  based on the phosphate analysis results clarified lasting questions of the original function and purpose of promontory forts.

Johanna Ullrich, Ph.D.