His adhesion brought ruin instead of strength to Hereward. If William
could afford to neglect a band of outlaws in the fens, he could not rest
with these two great earls in arms against him. There were forces in the
north to attend to Edwin; Morcar and Hereward must be looked after.

[Illustration: ELY CATHEDRAL.]

Gathering an army, William marched to the fen country and prepared to
attack the last of the English in their almost inaccessible Camp of
Refuge. He had already built himself a castle at Cambridge, and here he
dwelt while directing his attack against the outlaws of the fens.

The task before him was not a light one, in the face of an opponent so
skilful and vigilant as Hereward the Wake. The Normans of that region
had found him so ubiquitous and so constantly victorious that they
ascribed his success to enchantment; and even William, who was not free
from the superstitions of his day, seemed to imagine that he had an
enchanter for a foe. Enchanter or not, however, he must be dealt with as
a soldier, and there was but one way in which he could be reached. The
heavily-armed Norman soldiers could not cross the marsh. From one side
the Isle of Ely could be approached by vessels, but it was here so
strongly defended that the king's ships failed to make progress against
Hereward's works. Finding his attack by water a failure, William began
the building of a causeway, two miles long, across the morasses from the
dry land to the island.

This was no trifling labor. There was a considerable depth of mud and
water to fill, and stones and trunks of trees were brought for the
purpose from all the surrounding country, the trees being covered with