The Brenig dam was built in the early 1970s to control the flow of water in the River Dee and provide a water supply for the area around Llangollen, Wrexham, Chester and Merseyside. The dam was designed for minimum impact. It has an earth face and a mound in the middle which has been planted with trees to break up the line.
The spruce forests around it were planted at the same time and should have been clear felled in the early 1990s. By that time, though, the lake had become a tourist attraction, with boating and water-skiing on the lake itself and paths for walkers and cyclists through the woods. The trees are still being harvested but on a longer cycle. Broadleaved trees are being planted on the lake edge and along the paths. The woods are home to a range of wild animals, even including a few red squirrels.
The construction of the dam also inspired archaeological exploration of the area around the proposed reservoir. During the Bronze Age, in the 2nd millennium BC, the valley was a huge ritual site, with cairns, burial mounds and circles of wooden posts. Later, during the medieval and early modern periods, there was a farmstead on the east side of the valley and a number of hafodai, huts for people looking after sheep and cattle on the summer pastures. But the most exciting find was to the north-east of the reservoir. Over 7,500 years ago, wandering hunters camped here and left flakes from their flints and charcoal from their fires for the archaeologists to find.
Most of the sites on the east shore of the reservoir have been restored and a waymarked archaeological trail takes you around them. There are detailed interpretative boards at each site, and a leaflet describing all the sites is available from the Visitors’ Centre. To follow the whole trail, walk along the forest track on the east side of the reservoir for about 21/2 miles, to the ruined farmstead called Hafotty Sion Llwyd. This is an old hafod, a summer shelter. It was rebuilt in 1881 (the date is on the lintel of the right-hand window) using stone from the medieval farmstead of Hen Dinbych on the hill above. You will see the ruins of Hen Dinbych later on. Hafotty Sion Llwyd was the home of the bailiffs and shepherds of the sheep-range in the valley. There were legends of fairy gold and fairy music at the farm.
Continue on the forest track for another half-mile. Just before the car park, there are two burial mounds between the track and the shore. The first is a ring cairn, a low, solid stone ring surrounded by a circle of posts. These posts may originally have been carved, but there is no evidence for this. The ring cairn was originally a ceremonial structure. Rituals practised there included the burial of charcoal in pits. Some years later the cairn was used for burials. A little nearer to the car park is Boncyn Arian, ‘Money Hillock’. This mound covered a series of burials and a complex strucure of wooden stake circles and a dry-stone wall. One of the burial urns contained only the burnt ear bones of an infant - was this a strange sacrifice? (Why do archaeologists assume that things we can’t understand were rituals - and gruesome rituals at that?)
Between the two cairns and nearer the road is the Mesolithic hunters’ camp site. There is nothing to be seen there now, but the site has been marked with a stone. Across the lake you may be able to see three more barrows, two on the mainland and one on the little island.
Cross the stile on the other side of the track and walk up the little Nant Criafolen. As you get nearer to the trees, you can see on either bank the foundations of several small buildings. These were hafotai, summer huts dating from about the sixteenth century. The circle of wooden posts near one of the hafotai marks a circle of prehistoric post-holes. These were probably all that remains of a small prehistoric building, possibly a house.
Follow the waymarks along the forest edge. The route goes down into the little valley above Hafotty Sion Llwyd and up the other side. At the top of the slope is a large and complex platform cairn. Underneath this, the archaeologists found black soil, charcoal and fragments of pottery. In the early Bronze Age - about 2,000 BC - people were living here. Some of the field boundaries which criss-cross the slopes may be theirs. Then the valley became a ritual place with stone rings and burial mounds.
The platform cairn was originally built as a wide ring of stones with an open centre. There was a post of some sort in the middle, possibly for something like a maypole. The stones covered the burial of an adult and a child. Their cremated bones were placed in an urn under a large stone in the southern part of the cairn. Then the centre of the ring was used for another cremation burial. Later again, the centre was filled in with stone to make a platform. Finally, a small semi-circular cairn was added on the north-east edge to cover a small pit with an urn containing only charcoal.
From the platform cairn, bear round the slope to the right to look down over Hen Dinbych. This large enclosure contains the ruins of several buildings. The large one to the south was probably a substantial farmhouse, though some people have suggested it may have been a church. There were smaller buildings in the northern part of the enclosure. The slopes above the farm are laid out in terraced and embanked fields.
You can reach this point directly from Hafotty Sion Llwyd. Turn right off the main forest road to walk up the track past the farmhouse. Bear right with the track and follow the waymarks up to another Bronze Age kerb cairn. The boulders in the kerb are so large that they were once thought to be a small stone circle. Excavation found that they were the kerb of a cairn over a large rock-cut grave pit with a cremation burial. From this cairn you can walk up the slope to your left to the platform cairn or contour around to the slope above Hen Dinbych.
Walk through the site of Hen Dinbych, through the gate to your left, along a hollowed lane and over the stile. Follow the waymarks across the flat valley bottom. Ahead of you is a small kerb cairn. The ring of large stones would have held together a cairn of smaller stones covering a cremation burial. This cairn was built over the the post-holes of another prehistoric building, possibly a house. The large stone further down the valley is Maen Cleddau, the Sword-stone. It is a glacial erratic with a fragment broken off it. According to legend, this was sliced off by a giant’s sword.
More details of the landscape and archaeology of this area on the Clwyd-Powys Archaeological Trust site.