Reasons for Designation
Blockhouses are defensive structures of widely varying design built
specifically to house a small artillery garrison and to protect the gunners
and ammunition from attack. Usually stone built, each structure was designed
and built to protect a particular feature or area; typically they were located
to command a river, harbour entrance or anchorage. The main components of
blockhouses were a tower and bastions or gun platforms, although in some cases
only the tower or the bastion was present.
The earliest known blockhouse dates to 1398, but the majority were built in
the first half of the 16th century by Henry VIII. Distributed along the east,
south and south west coasts, there are 27 examples which are known to survive
in various states of repair, mostly now destroyed or incorporated into later
military constructions. Surviving examples will illustrate the development of
military defensive structures and of tactics and strategy during this period
of rapid change following the introduction of firearms. They will also
preserve something of the life and experience of the common soldier who was
required to live and work within them. All examples with substantial
archaeological remains are considered to be of national importance and will be
worthy of protection.
The Tudor blockhouse 300m south of Mersea Stone is the only example with
upstanding earthworks in Essex, although fragments of others may survive
incorporated into later military defences. Its preservation as an earthwork,
within a stable waterlogged environment, indicates that buried features and
deposits are preserved in situ and will yield valuable information about the
construction of the blockhouse and the way in which it was used. The site has
a wealth of related documentation and the remains will illustrate the events
of both 1588 and 1648 when the blockhouse saw action.
The monument includes a Tudor blockhouse situated on Mersea Island in a
commanding position on the south bank of the mouth of the Colne estuary, on
salt marsh between the present beach and the sea wall.
The remains of the blockhouse include an earthwork of a roughly triangular
plan. The longest side of the earthworks to the west measures c.80m north
east-south west, at its widest the earthworks are 45m east-west. The earthen
banks are up to 1.5m high, breached in two places by sea erosion. The
earthwork remains (surveyed in 1982) of one of the three original gun
emplacements is visible as a widened area of the earthen bank at the eastern
apex of the triangle. The long western side of the enclosure has been modified
by the construction of the sea wall. The interior retains buried structures
relating to the garrison accommodation although they are partly masked by the
The blockhouse was commissioned by Henry VIII in 1543. It was one of three
structures located to protect the strategically important Colne estuary.
The other blockhouses, situated on the Colne at St Osyth and Brightlingsea,
are no longer visible, though they would originally have been operated in
conjunction with the fort at Mersea Stone. The monument at Mersea Stone is
well documented and is of particular interest because of its method of
construction. Documentary sources indicate that instead of stone the
defences were constructed of `earth and board'. Each long side of the
structure was 300ft long with semicircular gun emplacements, housing a total
of 12 guns, at the apex of each angle, while the interior of the enclosure is
known to have contained the garrison accommodation.
Its cannon were dismounted in 1553 but the blockhouse was repaired to counter
the Armada in 1588 and again in 1631, when Dunkirkers threatened the Essex
coast. It played a part in the Civil War, in 1648, when it was captured by a
small number of Parliamentarian dragoons, allowing their men to sail up the
Colne during the siege of Colchester. At this time it was repaired once again,
its ramparts being reinforced with turf. In 1655 Cromwell ordered its
demolition but the owner of the land forbade its destruction.
There are no exclusions.
The site of the monument is shown on the attached map extract.
It includes a 2 metre boundary around the archaeological features,
considered to be essential for the monument's support and preservation.