Melvyn Bragg and guests discuss megaliths - huge stones placed in the landscape, often visually striking and highly prominent. Such stone monuments in Britain and Ireland mostly date from the Neolithic period, and the most ancient are up to 6,000 years old. In recent decades, scientific advances have enabled archaeologists to learn a large amount about megalithic structures and the people who built them, but much about these stones remains unknown and mysterious. With Vicki Cummings Professor of Neolithic Archaeology at the University of Central Lancashire Julian Thomas Professor of Archaeology at the University of Manchester and Susan Greaney Lecturer in Archaeology at the University of Exeter.