St Paul’s Cathedral is the City of London’s most important monument and historic building. But Wren’s great work is only the most recent of a succession of Anglo-Saxon and medieval cathedrals on the site, where Christianity was first established in AD 604. This report is the first ever comprehensive account of the archaeology and history of the cathedral and its churchyard from Roman times up to the construction of the Wren building which began in 1675. Archaeological excavations and observations go back to the time of Wren. The Anglo-Saxon cathedral is an enigma, and even its precise site somewhere in the churchyard is not known for certain. The medieval cathedral was probably the largest building in medieval Britain and one of the largest in Europe, with its 400ft-spire and a rose window to rival those we now see at Notre Dame in Paris. Recent excavations in and around the Wren building are described, and some of the many architectural fragments of the medieval cathedral, dug up over the last 150 years, are studied. Documents, surveys and early maps show the development of the religious complex and illuminate the lives of its occupants. In the 1630s a classical portico was added to the west end by Inigo Jones, Britain’s first truly Renaissance architect. Fragments of the portico, still covered with the soot of the Great Fire of 1666 which destroyed the cathedral, were found in 1996 when a tunnel was dug through one of the crypt walls of the present building. From these varied sources, the cathedrals which preceded that of Wren come to the surface again, and we can appreciate the cultural and religious importance of St Paul’s within the City of London, over a period of more than 1000 years.