canal into sections, maintaining the required depth of water, with goods transhipped or boats dragged across the barriers. They may also have been a deliberate precaution against the whole section drying out in summer. Conversely, Grahame Clark established that certain of these gravel causeways, at Cottenham, originated in the fourth century as a precaution against flooding, after the canal had gone out of use for transport. It acts as a catchwater drain in parts, intercepting runoff from the higher ground to the west: evidence of seventeenth-century improvements to form part of local drainage schemes has been identified, overlying material from the Roman period. Conversely, the southern half of its passage through Lincolnshire and its northern end, near Washingborough, are accepted as having had a raised bank on each side; the one on the upland side would not be a feature well adapted to a catchwater drain. Both these interpretations could be correct: Macaulay and Reynolds (1994) suggest that the effect of both deliberate re-cuts in the late Roman period to improve land drainage, and the natural flows of surface water along some sections of the route, resulted in the change of use from transport to agricultural improvement. It is possible to trace features that could be interpreted as boundaries all round The Fens which are either of Roman date or natural. In c.120 AD the Roman emperor Hadrian visited Britain and the sections dating from this period may be associated with his plan to settle the Fens. The exception is in the south-east of the Fens where the landscape was manually strip mined for phosphate so destroying any evidence, before the days of detailed mapping and aerial photography. One conclusion, though given the conflicts in the surviving evidence one not reached by everyone, is that overall it was used primarily as a boundary, (as part of it in south Lincolnshire undoubtedly was in the medieval period) but that parts were adapted to serve also as a catchwater drain. Although possibly not originally intended as a means of transporting goods, archaeology has demonstrated that, in some parts at least, it was used by cargo-carrying vessels. In his historical novel Imperial Governor, , George Shipway maintains that Gaius Suetonius Paulinus, then governor of Britain, conceived draining the fens as a way of denying Icenian rebels a place to hide. Route The northern part of the Car Dyke from Lincoln to Peterborough is