An area excavation was undertaken in December 2004May 2005 within the western part of the interior and defences of Metchley Roman fort, Birmingham (central England) in advance of proposals for a new hospital development. This was the largest single excavation of the fort interior undertaken at Metchley, comprising an area of approximately 0.4ha, equivalent to approximately 9% of the total internal area of the Phase 1 and Phase 3 fort. This volume, the fourth in the reports, concentrates on the researches into the western fort interior, defences, and post-Roman activity.A report on excavations which provide evidence for the entire military sequence at the Roman fort of Metchley. A wide range of features and feature types were sampled, including defensive ditches and gatehouse structures, timber-framed buildings and industrial features.