Tomen y Mur is a Norman earthwork castle built on the site of a Roman fort. Conspicuous for miles around, the mound offers great views of Trawsfynydd Reservoir and the surrounding countryside. Several features remain from the Roman fort, which was built in AD78 during Agricola`s campaign in Wales. Later rebuilt in stone, it was abandoned about AD140. Near the car park in the lane off the A470 is an overgrown oval ampitheatre, probably used for weapons training, and Sarn Helen, a Roman road.