The thought of the Fenland Abbeys leads on to the fascinating story of the draining of the fens. For the monks were the first to reclaim from the morass such little patches of ground as each Abbey could bank in, and to discover how very fertile such reclaimed soil is. Their early chronicles speak with rapture of the hay that could be mown three times a year, and the amazing fecundity of the corn-land. Thus it was their interest constantly to be enclosing fresh acres. They discovered, too, that by judiciously letting in the flood water on to a field they could get a fresh deposit of silt, and gradually raise the level of the soil. And the first attempt at drainage work on a large scale was also due to a monk, Bishop Morton, Abbot of Ely, who in 1480 cut the twelve mile long "Leam," or channel, which still bears his name, to divert the River Nene from its long meandering course through Whittlesea Mere and Outwell, and to bring it straight to Wisbech. Thus it came about that the reclamation of the fens went hand in hand with the prosperity of the Abbeys around them. When these were prosperous, the whole district prospered; when misfortune befell them, the fens likewise suffered; and it often took many years for the marks of the ruin to be effaced. After the wholesale destruction wrought by the great Danish raid of 870, centuries did not suffice for this. The story we have just told of the sack of Crowland clearly shows that the place was then accessible by land. But in the hundred and fifty years of desolation that followed, such works as the brethren had effected fell into decay, and the land once more became waterlogged. Even when William of Malmesbury wrote, in the twelfth century, he tells us that Crowland could still only be reached by boat. And the yet more wholesale destruction wrought by Henry the Eighth was followed by a like period of reversion to waste. The zeal, however, of these early civilisers was not always according to knowledge; and at quite an early date a grievous mistake was made, which caused endless difficulties ever after, and still affects the whole drainage system of the district. This was the cutting, at some date between 1215 and 1270, of a leam, not two miles long, from the Great Ouse at Littleport to the Little Ouse,[241] thereby diverting the waters of the former into the channel of the latter, and bringing their united volume into the sea at Lynn. Before that date the Great Ouse ran from Littleport to Outwell, where it was met by the Nene, and by a branch of the Little Ouse. The joint river was called the Well Stream, and poured into the sea at Wisbech. [Footnote 241: The Little Ouse drains the south-western districts of Norfolk.]