Having suffered depredation of the more movable stones of the site, the monument was excavated by W J Hemp in 1928–29. He revealed much of the sequence of use on the site, and found the 'Pattern Stone'. It has since been moved to the National Museum of Wales and replaced with a replica standing outside the back wall, but within the area of the original mound, and close to the spot where it was found. The Pillar was set back upright, and the earth and stone mound covering the passage and chamber was reinstated, but clearly there was much less material available than had been used originally. Some additional concrete roof supports have also been added at some point.