In the course of a paper on ‘Roman Colchester’ in volume ix of this Journal, Mr. Philip Laver and the writer drew attention to the vaults which underlie Colchester castle, and claimed for them a Roman origin. The claim is based primarily upon constructional evidence which is readily appreciated in the presence of the actual remains, but the published summary perhaps requires some amplification for the reader who is unacquainted with these. Until its recent acquisition for the Colchester Corporation, the castle was in private possession, and was only partially known to the public; nor does the mass of literature which has gathered round the structure include any detailed study of its architectural problems. Hence the dark and comparatively barren vaults have hitherto escaped more than passing notice.