Llan-gors crannog lies in the largest natural lake in south Wales (Llyn Syfaddan), within the former early medieval kingdom of Brycheiniog. Concerns in the 1980s about erosion and recognition that submerged organic materials were well-preserved culminated during the summers of 1989-93 in a programme of fieldwork and excavation by the Museum and Cardiff University. In 2004 a joint Museum/Marine Archaeological Research Consultants/Giffords team conducted further underwater archaeological work in advance of a conservation scheme funded by Cadw, the historic environment agency of the Welsh Assembly Government which was co-ordinated by the Brecon Beacons National Park Authority. These fieldwork programmes are resulting in a complete reassessment of the site and its place in Welsh history. The excavations established that the island had been periodically extended from an initial D-shaped platform constructed of sandstone blocks resting on brushwood, branches, and timber. The site can now be identified with the place known to the Saxons as Brecenanmere, built between the years AD 889 and 893 destroyed by a Mercian army in AD 916. The tight dating of the site (in use for about 25 years) makes it a time capsule and microcosm of live on a royal llys during the late 9th and early 10th centuries.
The post-excavation research programme is characterising the site and its well-preserved material culture, which includes organics and textile (some of exquisitely decorated with small lion and bird motifs), jewellery and evidence for bronze casting. The palaeo-economy is one important research focus. Anatomical representation and butchery of domestic animals, their aging and sexing, and the occurrence of wild animals indicate that cattle, sheep and pig provided food, alongside red deer, roe deer, wild boar and rabbit — evidence of livestock rearing, possibly the taking of tribute in the form of food render, and hunting. Analyses of metalworking residues, metallurgy and timber are shedding light on royal patronage and woodland management.