Lex Bosman is Professor of Architectural History at the University of Amsterdam, with a special interest in Early Christian and Medieval Architecture. He has been a fellow of the Royal Netherlands Institute in Rome and Scholar in Residence at the Istituto Universitario Olandese di Storia dell'Arte in Florence. He is the author of many publications, including The Power of Tradition: Spolia in the Architecture of St. Peter's in the Vatican (2004). Ian Haynes is Professor of Archaeology at Newcastle University, specialising in Roman Archaeology. He has directed twelve field projects in five countries and in 2019 was awarded an ERC Advanced Grant for a five-year investigation of SE Rome. He is the author or editor of eight books including Blood of the Provinces (2013). Paolo Liverani was Curator for Classical Antiquities at the Vatican Museum and is now Professor of Ancient Topography at the University of Florence. He is the author of eight books, including The Vatican Necropoleis (2010).