The excavation of Verulamium in the years 1930–4 originated in a coincidence of archaeological need and local opportunity. The former, at this late date, needs no elaboration; the latter, it may be recalled, lay in the acquisition, by the Borough of St. Albans, of the southern half of the walled site, now known to have taken shape in the second century A.D. A central area within the new Corporation property accordingly remained for three years the main focus of the excavations, supplemented by an intensive examination of the town-defences, including two wall-towers and three gateways, of which two lay on property retained by Lord Verulam.

Archaeologically, the problem confronting the excavators was twofold: to establish (for the first time) the outlines of the economic history of a major Romano-British town deep-set in the 'lowland zone'; and to determine the relationship, topographically and culturally, of the successive Belgic and Roman settlements. It was a familiar fact that Verulamium had held an important royal mint at the beginning of the first century A.D., and, whether the term municipium applied by Tacitus to the town in A.D. 61 be taken at face-value or no, the chance of observing the growth of a first-class Roman city out of a first-class pre-Roman one was unsurpassed on any other site. It was, therefore, essential that the exploration of a part of the Roman city should be accompanied by a systematic search for its predecessor.