Few Welsh prehistoric sites capture the imagination as powerfully as Tre'r Ceiri hillfort which dominates the Llyn Peninsula from the easternmost summit of the three-peaks of Yr Eifl. Looking down from a scree-strewn summit at a height of 485m O.D., Tre'r Ceiri is one of the best preserved Iron Age hillforts in Britain where round houses, gateways and ramparts can be seen in a remarkably intact condition.
Tre'r Ceiri occupies a steeply-sloping site whose summit is occupied by a substantial Early Bronze Age burial cairn, clearly preserved and respected within the later hillfort. The main hillfort is enclosed by a formidable single rampart which still stands up to 3.5m high in places. Where nearly intact, the top of the rampart still has its parapet walk reached via a number of sloping ramps from the interior. This wall is broken by two main gateways, both of which funnelled visitors through narrow, restrictive passages, as well as three `posterns' or minor gateways, one of which at least was designed to allow inhabitants out down a narrow mountain path to gather water from a spring. Beyond the main hillfort is a second partial outer wall, reinforcing more vulnerable approaches on the north and west sides. This too is broken by an outer gateway which overlies an earlier approach track to the hillfort, probably indicating that this outer defence was a secondary work.
As befits one of Britain's finest hillforts there have been many visits to, and surveys and excavations of, Tre'r Ceiri over the centuries. During the 1950s, A H A Hogg and officers from the Royal Commission conducted several campaigns of excavation and survey at the Caernarfonshire hillforts to clarify their development for the (then) forthcoming three volumes of the Caernarvonshire Inventory. Together with W E Griffiths, Hogg completed a full survey of Tre'r Ceiri in 1956, complete with contours and details of surrounding hillslope enclosures, building upon Harold Hughes's pioneering measured survey of 1906. This was immensely detailed, yet clear, and was only superseded by a modern total-station survey of 1980. We know from excavations, by Hogg and others, that the hillfort was probably constructed in the later Iron Age and remained in use until at least the 4th century AD, the late Roman period. Other prominent stone-built hillforts on Llyn, principally Garn Boduan and Carn Fadrun, have very late-phase stone citadels on their highest summits which are thought to have been castles of medieval Welsh princes; Tre¿r Ceiri lacks any similar evidence.
In 1989, Cyngor Dosbarth Dwyfor and Gwynedd County Council, with funding from Cadw, began a long programme of consolidation and repair of the fort with archaeological supervision provided by the Gwynedd Archaeological Trust. The project ran for a decade, often through the most adverse of weather conditions, leaving this most intriguing of hillforts renewed and ready to endure another two thousand years of life.
Sources: Baring-Gould and Burnard in Archaeologia Cambrensis IV (1904), 1-16
Hughes in Archaeologia Cambrensis VII (1907), 38-2
Hogg in Archaeological Journal 117 (1960), 1-39
RCAHMW Caernarvonshire Inventory II (1960), 101-3
For more recent excavation & restoration see: Archaeology in Wales 31 (1991), 16; 32 (1992), 57; 33 (1993), 49-50; 34 (1994), 46-7; 38 (1998), 98.
T. Driver, RCAHMW, 6th Aug 2008