A watching brief by Colchester Archaeological Trust on drainage works and depth-limited soil-stripping within a large compost-production site at Birch airfield resulted in the discovery of linear features and pits dating from the Late Iron Age/early Roman period onward. The fieldwork was prompted by the enlargement of the compost hardstanding area and improvements to the site drainage. These involved ground-stripping over a total area of approximately 7,500 sq m together with excavations to create a 3m-deep lagoon fed from a new 200m-long ditch. The first phase involved investigation of the sites for a proposed 3m-deep lagoon (Area 1) and a 200m-long feeder ditch (Area 2). This commenced with archaeologically controlled soil-stripping in which topsoils were progressively removed by machine down to the uppermost archaeologically sensitive level. At that point, exposed ground features were manually investigated to establish their character and date. The second phase of fieldwork was concerned with soil-stripping in an adjoining area of 6,500 sq m which is to be used as hardstanding (Area 3). The evidence included ditches and gullies belonging to field systems, possibly with associated structures. The nature and distribution of finds suggest that a focus of Roman occupation lies within or in the immediate vicinity of the northwestern region of the airfield. <1>