154 NOTES ON ANCIENT DEFENSIVE EARTHWORKS.
always have seemed the best in that district as the place for a
camp of refuge. The surface of the ground occupied by the
town of Rayleigh is almost all of it more than 200ft. above the
sea, the greatest elevation I have seen noted on the map being
276ft. This gives a healthy elevation in a district bounded by
the once ague-haunted marshes of Canvey Island on the south,
and by those of the Crouch and its tributary the Roach on the
north and east. And it must always have had a decided advan-
tage over the London Clay area around as regards water supply,
that obtainable here and there from the uppermost beds of the
London Clay being usually unpleasant, while the rest of that
formation yields none whatever. In ancient times this district
was peculiarly accessible to piratical marauders, who might come
up the Roach, the Crouch, or the Thames. The town of
Rayleigh stands about midway between Benfleet on the south,
where Alfred destroyed the Danish fleet, and the highest point on
the Crouch, northward, to which sea-rovers were likely to bring
their ships. The Castle is on a promontory of the high ground
which juts out westward from the main mass, so as to afford a
better natural site for a stronghold than could be expected in
Essex. If somewhat inferior to a hill fort on the Chalk south of
the Thames in needing some artificial increase to the height of the
chief mound, it had an advantage over almost all of them as
regards water supply. For whereas Chalk camps are usually
dependent on the storage of rain water in "dewponds," at
Rayleigh water oozes out at the junction of the London Clay
with the overlying Bagshot Sands east of the Castle mounds, and
supplies the large pond within the outer works, which I am
informed is never dry in the driest season.
Mr. G. T. Clark, writing on "Moated Mounds or Burhs"
in the Archaeological Journals remarks that "these Burhs are not
like British earthworks placed on the tops of hills,
nor like Roman stations upon main roads ; they were the
centres of large Saxon estates, the seats of great landowners."
(Archaeological Journal, Vol. 46, p. 197, 1889,). And in a previous
paper (Vol. 38, pp. 26-7), he says that they were thrown up in
the ninth and tenth centuries for the defence of private estates,
and that they are not governed to any great extent by the
character of the ground. As Essex examples of Burhs, he gives,
in the latest of the papers mentioned, "Blethebury," (?)4 Mount
3 Vols. 24, 38 and 46.
4 This is the name given in Clark's paper, "List of Burhs," Archaeol. Journ., vol. 46,
p. 203. But I must confess that I cannot find out where it is, though Clark adds—" A seat of
the Anglo-Saxon Kings. Banks and ditches. Qy. Mound."