Having thus come to know something of Ely Minster, we shall feel the greater interest in all our further explorations through those highways and byways of the surrounding district over which she presides with the air of a Mother, and a Queen. [Illustration: _Willow Walk._] CHAPTER XVIII Boundary of Fens.--Roman Works, Car Dyke, Sea Wall, Causeway.--Archipelago.--Littleport, Agrarian Riots.--Denver Sluice.--Roslyn Pit.--Fenland Abbeys, Chatteris, Ramsey, Peterborough, Thorney, Crowland. The vast Fenland district of which the Isle of Ely is the core consisted, until the fens were drained, of an archipelago of scattered islets rising out of a morass, through which the rivers from the uplands around stagnated in a complex system of waterways, constantly changing, as one branch or another got silted up and the streams had to make themselves new channels. The foreshore of the uplands may still be traced on a contour map, and is seen to be deeply indented, with bays running in from the fen and capes running out into it. The southernmost point of the morass was at Fen Ditton on the Cam, two miles below Cambridge. Its western boundary went by, Waterbeach, Cottenham, and Willingham, to Earith; thence through Huntingdonshire to Ramsey and Peterborough; thence, by Deeping, Holbeach, and Spalding, to the Witham, a few miles below Lincoln. Throughout all this length ran a Roman earthwork, the Car Dyke, still existing at many points, evidently thrown up by these mighty civilisers to keep the floods in check. A like Roman embankment, of much larger dimensions, is to be seen on either shore of the great estuary which of old brought the sea-shore as far south as Wisbech. The eastern boundary of the Fenland needs no such defence, as on this side the higher ground sinks much more abruptly to the fen level. It passes from Fen Ditton by Horningsea, Bottisham, Swaffham, and Reach to Burwell. Here a peninsula projects to Soham, followed by a deep inlet to Isleham and Mildenhall. Then it runs north and west to Downham, in Norfolk, and thence due north to the sea by Lynn.