A seminal study of the long barrows authored by the Welsh archaeologist Glyn Daniel was published in 1958 as The Megalith Builders of Western Europe.[29] In 1950, Daniel stated that about a tenth of known chambered long barrows in Britain had been excavated,[52] while regional field studies helped to list them.[52] Few of the earlier excavations recorded or retained any human remains found in the chamber.[17] From the 1960s onward, archaeological research increasingly focused on examining regional groups of long barrows rather than the wider architectural tradition.[29] From this decade onward, the meticulous excavation of various long barrows also led to the widespread recognition that long barrows were often multi-phase monuments which had been changed over time.[29]