The Roman military site at Longthorpe, west of Peterborough, was discovered by observation from the air in 1961: no traces now remain on the surface. Excavations between 1967 and 1973 have shown that a 27-acre fortress with timber buildings, accommodating a legionary vexillation together with auxiliary troops, was succeeded by an 11-acre fort. The period of occupation extended from c. 44/8 to c. 62. Crop marks observed from the air at Orton Stanch, 400 m. south-east of the fortress, have led to the discovery of a native farmstead. Excavations there by Messrs. A. Challands, G. B. Dannell and Dr. J. P. Wild have shown that agricultural activities were intermitted for the period of the occupation of the fortress, the settlement being replaced by a large industrial establishment or worksdepot involved in pottery manufacture and possibly in bronze-working with clear military connections. The present report describes the excavation of the fortress: the industrial site is to be published in a future volume of Britannia.