2006:252 - DUNMORE HEAD, Horse Island, Kilbaha South, Clare

The rapid erosion of the promontory fort defences on the narrow isthmus leading from the mainland to Horse Island led to a rescue excavation on the isthmus over a two-week period in May 2006. The rescue excavation was necessary in order to record the morphology of the defences and also to obtain samples for radiocarbon dating before the evidence was lost through the rapid ongoing erosion. The radiocarbon dates will be helpful in clarifying the chronological position of promontory forts in Ireland.

There are the remains of at least two lines of defence on the isthmus. The inner defence is the more substantial and consists of a ditch, 4.5m wide and 1.5 deep, with a stone wall along its inner edge. The outer line of defence consists of an earthen bank with at least one, and possibly two, external ditches.

Three trenches were excavated: Trench A across the inner defences, Trench B across the outer defences, and Trench C which was positioned to further investigate a feature of the outer defences revealed in Trench B.

The excavation of Trench A was carried out to examine and record the details of the stone wall on the inner edge of the inner defensive ditch. The 1.5m by 1m trench was excavated to a depth of 0.85m and all sediments beneath the sod layer were sieved through 2.5mm sieves. Beneath several layers of stones and sediments, the intact 0.5m-high remains of a mortared stone wall were revealed. This wall formed the eastern side of the entrance to the promontory fort. The wall was over 1m wide and the entranceway had a curving splay that widened towards the interior of the fort. An in situ stone with a ‘mortise hole’ protruded from the base of the wall into the entranceway at the outer edge of the entrance (this may have held a wooden element of the doorway, such as a jamb). The entranceway appeared to be cobbled.

It had been originally proposed to extend Trench A from the wall through the defensive ditch, but this turned out not to be feasible due to further erosion of the cliff on the west side of the isthmus. However, because the different layers of the fill of the ditch were clearly exposed on the cliff face, it was possible, using an EDM, to record the stratigraphy of the ditch section on the adjacent cliff face. Samples of limpet shell, charcoal, burnt and unburnt bone were removed by hand, using a trowel, from the cliff face. These samples will be used to obtain a series of radiocarbon dates for the ditch fills. Finds from Trench A included shell, charcoal, mortar and some corroded iron pieces.

Trench B was excavated to examine and record the outer defences of the promontory fort, which appeared at first to consist of a single bank and ditch, and also to collect organic samples for radiocarbon dating. These outer defences are situated on the isthmus, c. 40m due north of the inner defence ditch at the entrance to the island. A 9.7m by 1m trench was excavated to a maximum depth of 0.9m. Exposed in this excavation trench was an earthen bank with an external ditch. A section of the natural substrate that spanned the ditch may have formed a causeway across the ditch. A layer of cobbles and stones on the northern side of the bank may be the remains of a wall and a deposit of mottled black and dark-brown silt with some old root casts under the bank may be an old turf layer that formed on top of an earlier bank.

North of the ditch, on the west side of Trench B, a feature that at first appeared to be the eastern half of a circular pit or large post-hole was revealed. In order to determine the extent of this feature, a small trench (Trench C, 1.8m by 0.8m) was excavated to the west of Trench B, leaving a narrow baulk between them. Only the sod and topsoil were removed in Trench C in order to reveal just the top of this feature in plan view. This showed that this feature is the eastern end of a further ditch or pit outside the primary bank and ditch (but not a large post-hole). Finds from Trench B were limited to some animal bone and iron fragments and small amounts of charcoal.

Leana, Killinaboy, Co. Clare and NUI Galway, Galway