The fourth season of excavation at Portus takes place between late March and early May 2011. As in previous years these have been undertaken by the University of Southampton, in conjunction with the British School at Rome and the Soprintendenza Speciale per i Beni Archeologici di Roma, and funded by the Arts and Humanities Research Council. The area chosen for excavation lies to the south of areas excavated in previous years, but still within the confines of the Palazzo Imperiale. To date they have revealed an extensive series of walls belonging to both the Palazzo itself and a large adjacent building, both of which were demolished in the late antique period, and which further contribute to our understanding of this unique complex. The team is directed by Simon Keay, assisted by Graeme Earl, and with the involvement of Fabrizio Felici (Parsifal Cooperativa, Roma), and staff and students from the Universities of Southampton and Rome and professional Italian archaeologists. The team also wishes to acknowledge the valuable support of Dott. Angelo Pellegrino (Soprintendenza Speciale per i Beni Archeologici di Roma, sede di Ostia).