"In the northern part of Cambridgeshire there is a vast extent of low and marshy land, intersected in every direction by rivers. All the waters from the centre of England which do not flow into the Thames or the Trent, empty themselves into these marshes, which in the latter end of autumn overflow, cover the land, and are charged with fogs and vapours. A portion of this damp and swampy country was then, as now, called the Isle of Ely; another the Isle of Thorney, a third the Isle of Croyland. This district, almost a moving bog, impracticable for cavalry and for soldiers heavily armed, had more than once served as a refuge for the Saxons in the time of the Danish conquest; towards the close of the year 1069 it became the rendezvous of several bands of patriots from various quarters, assembling against the Normans. Former chieftains, now dispossessed of their lands, successively repaired hither with their clients, some by land, others by water, by the mouths of the rivers. They here constructed entrenchments of earth and wood, and established an extensive armed station, which took the name of the Camp of Refuge. The foreigners at first hesitated to attack them amidst their rushes and willows, and thus gave them time to transmit messages in every direction, at home and abroad, to the friends of old England. Become powerful, they undertook a partisan war by land and by sea, or, as the conquerors called it, robbery and piracy." _A. Thierry, History of the Conquest of England by the Normans, book 4._