The most remarkable monument of Roman engineering in the Fens is the catchwater drain called the Cardyke (_Brit._ “fen-dyke”), which leaves the Witham at Washingborough about three miles from Lincoln, and then for eighteen miles takes a southerly course parallel to that river at distances varying from two to five miles from it. The primary object may have been to intercept the water of the numerous streams coming from the Kesteven uplands; but it was doubtless intended to be navigable, as its width at the water-level was 50 feet, and at its bottom 30 feet. On both sides was a raised bank, flattened at the top to serve the purpose of a road, and still in some places crowned with a modern road. In the parish of Heckington, nine miles due west of Boston, it makes a sharp turn to the south-west, and then skirts the western border of the Fen for over thirty miles, till, after a course of fifty-six miles, it joins the river Nene, half a mile south-east of Peterborough, and about five miles below the Roman town of Durobrivæ (Castor). In some parts the Cardyke has been obliterated, and in many it is now a mere ditch; but its whole course can be exactly traced, and for a few miles it is still used as a drain. The last eight miles are beyond the borders of our county; but within those borders Roman remains have been found in at least ten parishes through which it passes. No vestiges can be found of the seven forts alleged by Stukeley to have been raised along its course, but there is a camp at North Kyme, within a short distance. Even with the aid of forced labour—partly, perhaps, imported from the Continent—such a work must have taken many years to construct; and it may have been in progress during a great part of the century between Trajan and Severus (A.D. 100-210). Its long course, parallel to the canalised channel of the Witham, suggests that its northern portion was first undertaken to assist in draining the mere south-east of Lincoln. But when this object was accomplished, and the immense work was taken in hand of embanking the shores of the Wash, the canal would gradually be extended southward in order to provide an inland waterway past Lincoln, by the Fossdyke, the Trent, and the Ouse, to the northern capital at York. This measure could hardly have been contemplated until the Holland Fen was sufficiently dry to admit of causeways being made across it into Lindsey on the north and Norfolk on the east.