Dinas Dinllaen - Community Archaeology Project

  The Promontory Fort

Introduction | The Promontory Fort | Geophysics | Community Engagement

Dinas Dinllaen is the largest of a handful of coastal promontory forts located along the coastline of Gwynedd and Anglesey. Two ditches and three banks located at the narrowest point at the neck of the headland enclose an area of some 14 acres enclosed by a combination of steep rocky cliffs which is overlain in places by thick layers of glacial drift – material left behind after the melting of the glaciers.

The excavation examined the two outer ditches and banks, but not the inner bank; four trenches were excavated in total, one across each feature.
The excavations have provided a wealth of information about the chronological development of the defences. Several construction phases have been identified which relate to when ditches were re-dug, or banks strengthened.

Some aspects of the project are not yet complete. Material samples taken during excavation have yet to be processed, and it is also hoped to obtain radiocarbon dates for some of the phases from these samples.

The excavated evidence shows that during the first phase of construction the two banks would have been fairly insubstantial, as were the ditches. We cannot say for certain what size the ditches would have been at this point as the earlier evidence was lost when the ditches were subsequently enlarged. It is possible that these banks and ditches should be seen as symbolic boundaries as much as functional or defensive structures.

The second phase saw substantial enlargement of both banks and ditches. It is at this point that the ditches reached the size recorded during the excavation; the first (outer) ditch was about 6.5m wide and 2.5 deep, and the second about 5m wide and 1.4m deep. We know that the second ditch reached its maximum depth at this point as one of the last dumps of material placed on top of the second phase bank consisted of broken bedrock, which was dug out from the base of the ditch. At this point in time the first bank would have been at least 0.75m high and 4.5m wide, and the second 1m high and 7.7m wide. These defences would have been a substantial obstacle for anyone who attacked the fort, as well as a visual symbol of power.

Neither the first bank nor the ditches appear to have been modified beyond the second phase; however, the second bank was further strengthened in a third phase of construction. In this phase additional material was placed at the back of the bank. The material added was deposited in a number of thin, compacted layers; possibly suggesting that they built up where people (or livestock) were walking at the back of the bank. At the end of this phase the bank reached a width of 9.1m.

In the final, fourth, phase of development a wooden palisade was added to the second bank. The excavations showed that a slot was dug along the bank and posts were dug into the slot and supported by large packing stones. The posts are thought to have supported a continuous timber palisade.

At this final stage of development the site was a very formidable fortress. The geophysical survey showed that the third inner bank was also protected by a wooden palisade meaning that any attackers would have to negotiate both ditches and breach two substantial wooden walls with strong gates before gaining access to the interior.


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