The Roman Legionary Museum at Caerleon, since 1930 a branch gallery of the National Museum of Wales, stands within the legionary fortress of Isca above a plot of the still little-explored scamnum tribunorum in the dextral angle of the via principalis and via praetoria (FIG. 1). With confirmation in 1982 of proposals for the complete rebuilding of the museum to an enlarged plan, the National Museum undertook responsibility for the archaeological excavation of the affected area (some 290 m2) which, in part, was scheduled under the Ancient Monuments Acts. In several episodes, between October 1983 and March 1985, all was systematically reduced to the level of the natural ground surface (at a depth of some 2–3 m below the present surface). Pressure of time and funds required that, in the later stages of this work, much of the basal (mainly Flavian) stratigraphy was removed by machine to reveal the fullest possible plan of the primary timber buildings of which so little is yet known at Isca (PLS IV A and B).