river, stands the strong fortress of Tilbury, called Tilbury Fort,
which may justly be looked upon as the key of the River Thames, and
consequently the key of the City of London. It is a regular
fortification. The design of it was a pentagon, but the water
bastion, as it would have been called, was never built. The plan
was laid out by Sir Martin Beckman, chief engineer to King Charles
II., who also designed the works at Sheerness. The esplanade of
the fort is very large, and the bastions the largest of any in
England, the foundation is laid so deep, and piles under that,
driven down two an end of one another, so far, till they were
assured they were below the channel of the river, and that the
piles, which were shed with iron, entered into the solid chalk rock
adjoining to, or reaching from, the chalk hills on the other side.
These bastions settled considerably at first, as did also part of
the curtain, the great quantity of earth that was brought to fill
them up, necessarily, requiring to be made solid by time; but they
are now firm as the rocks of chalk which they came from, and the
filling up one of these bastions, as I have been told by good
hands, cost the Government 6,000 pounds, being filled with chalk
rubbish fetched from the chalk pits at Northfleet, just above
Gravesend.

The work to the land side is complete; the bastions are faced with
brick. There is a double ditch, or moat, the innermost part of
which is 180 feet broad; there is a good counterscarp, and a
covered way marked out with ravelins and tenailles, but they are
not raised a second time after their first settling.

On the land side there are also two small redoubts of brick, but of
very little strength, for the chief strength of this fort on the