Iona was a major European intellectual and artistic centre during the seventh to ninth centuries, with outstanding illustrated manuscripts, sculpture and religious writings produced there, despite its apparently peripheral location ‘at the ends of the earth’. Recent theological discourse has emphasised the leading role of Iona, and particularly its ninth abbot, Adomnán, in developing the metaphor of the earthly monastery as a mirror of heavenly Jerusalem, allowing us to suggest a new appreciation of the innovative monastic layout at Iona and its influence on other monasteries in northern Britain. The authors contend that the unique paved roadway and the schematic layout of the early church, shrine chapel and free-standing crosses were intended to evoke Jerusalem, and that the journey to the sacred heart of the site mirrored a pilgrim’s journey to the tomb of Christ. The key to this transformative understanding is Charles Thomas’s 1956–63 campaign of excavations on Iona, which this article is publishing for the first time. These excavations were influential in the history of early Christian archaeology in Britain as they helped to form many of Thomas’s ideas, later expressed in a series of influential books. They also revealed important new information on the layout and function of the monastic complex, and produced some unique metalwork and glass artefacts that considerably expand our knowledge of activities on the site. This article collates this new information with a re-assessment of the evidence from a large series of other excavations on Iona, and relates the results to recent explorations at other Insular monastic sites.