Most writers have seen the Car Dyke as a navigable Roman canal, connecting the fenlands of Cambridgeshire and Lincolnshire with the major Roman markets of Lincoln and York. Its course is shown on the Ordnance Survey Map of Roman Britain as running from Waterbeach on the Cam to Washingborough, a few miles below Lincoln, on the Witham, and many, following Stukeley, have seen it as supplying the northern markets with the agricultural produce of the Roman fenland. The importance of cereals in this trade has indeed been questioned, but the general theory has persisted.
In order to assess the validity of the theory, and to establish the purpose of the work and the date and method of its construction, the northern half of the Dyke, from the Witham to Bourne, a distance of about 36 miles (57-6 km), has been studied over a period of some 10 years. This paper summarizes the findings to date. It is, of course, realized that all the conclusions reached here do not necessarily apply equally to the southern end.