The Isle of Iona, located off the south-western coast of Mull in the Inner Hebrides, has been described by the poet Robert Crawford (b. 1959) as a place where ‘spirit, imagination, and physical exertion mingle’. Iona’s assemblage of early medieval carved stones and grave slabs constitute a special part of the island’s magic, forming a collection of early medieval art for which there are few parallels in the rest of Europe. The importance of one cross in particular – the 8th-century Cross of St John – has only recently been realised, in part because of a study of its concrete replica, as Current Archaeology’s Chris Catling reveals.