THE EXCAVATION OF THE
GRAVESEND BLOCKHOUSE, 1975-76
D. THOMPSON AND MRS. V. SMITH
INTRODUCTION
After King Henry VIIl's break with the Pope, the possibility of
invasion from the Continent led to the building of a system of coastal
fortifications from Hull to Milford Haven, among them being five
small blockhouses in the Thames estuary, the order to build these being
given in 1539.
Of these five blockhouses, one was built at East Tilbury and one at
Higham, although neither of these are now in existence so far as can be
ascertained. Another was built at Tilbury (now buried under the
curtain wall of Tilbury fort) and the remaining two at Gravesend, one
(Milton blockhouse) at the western end of the canal basin and the other
at the site of the Clarendon Royal Hotel. It is this last one which is the
subject of this paper.
This historical background to this blockhouse has been published in
Arch. Cant., lxxxix (1974), (V. T. C. Smith, 'The Artillery Defences at
Gravesend') and should be read in conjunction with this paper.
THE STRUCTURE
The overall dimensions of the building were approximately
28 x 21 m.; of two storeys, it was built upon a substantial chalk raft.
Its construction was predominantly of brick, the external wall faced
with ashlar blocks. The ground plan consists of a D-shaped front,
behind which there is an oblong section; the walls then converge to
form the apex of a triangle to the rear.
Internally, there were two parallel walls: the first bisects the building
midway to form the rear portion of the D-shaped front, the other
forms the base of the triangular rear portion of the blockhouse. In
addition, a small D-shaped bastion is sited towards the rear on the west
side of the structure.
That the front portion of the building extended into the river is
shown by the existence of a river wall, which runs at right angles and
extends up to the wall of the blockhouse at a point approximately eight
153
D. THOMPSON AND MRS. V. SMITH
metres behind the front of the structure. This river wall will
subsequently be referred to as the 'old river wall'.
The site (N.G.R. TQ 650743) is situated under the lawn and car park
in front of the Clarendon Royal Hotel, and the excavation was carried
out by the Thameside Archaelogical Group under the joint direction of
Mrs. V. Smith and Mr. D. Thompson, on behalf of the Kent Defence
Research Group of the Kent Archaeological Society.
Investigations were commenced on 19th July, 1975, by carrying out a
probe survey of the area, but this failed to establish any significant
irregularities to indicate where excavation should begin. However, by
superimposing a plan drawn in 1715 onto a modem survey map of the
area, the locations of the walls could be predicted and the excavation
was started.
THE EXCAVATION
The sea wall running across the northern end of the site was taken as a
base line (A.O.D. 13·31 - 4·05 m.), offsets of 40 m. were taken at
points 4 m. west of the extreme easterly corner of the present sea wall
Gunction of the lawn and car park) and a further 17 m. west of this
point; the area of excavation was thus enclosed in a rectangle
17 m. x 40 m. that we anticipated would make available the northwest
quadrant of the building. After removing the turf and topsoil the
area was found to be covered by a layer of chalk and compressed
rubble, the remains of the Victorian pleasure gardens and tennis courts
occupying the site, which when removed showed that they had been
laid directly upon the destruction level of the blockhouse.
Subsequent excavation of this mass of debds, which completely filled
the remaining undestroyed lower portion of the building, provided the
following results:
1539, the exterior wall, period I (Figs. I and 2, Wall I)
This wall is the north-west half of the D-shaped front of the
blockhouse and the principal remaining wall of the Tudor period. It is
2 m.-wide and survives to a height of 2·70 m. of brick construction
faced with large rectangular blocks of ashlar. An offset 11 cm.-wide
and 23 cm. below the existing top of the wall, runs parallel with the
entire length of the excavated outer face with the exception of two
points, a short gap of 17 cm. adjacent to the old river wall, and the
other where this offset rises vertically for 57 cm. Unfortunately, this
feature could not be pursued owing to the limitation of the excavation
area. Between the shaped blocks of ashlar forming the offset and the
stonework immediately below was a packing of oyster-shells, which
154
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Fig. I. Plan of Excavation.
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Fig. 2. East-West Section through Excavation.
EXCAVATION OF THE GRAVESEND BLOCKHOUSE, 1975-76
only occurred on the portion of wall behind the river wall. A number of
mason's banker marks (Fig. 3, a-i) were found on the stonework in the
area. Apertures, presumably gun-ports, although bricked-in at a later
period could be clearly discerned. Two other apertures were also visible,
one of which had a large stone slab on the outer edge held in place by
iron staples on either side. These could possibly have been windows as
their position would have made them impracticable for use as gun
emplacements. The inner face of the wall was excavated to a depth of
2· 30 m. A brick-built platform protruded from this inner face l ·07 m.
below the existing top and extending to the base. This platform was
44 cm. wide and followed the entire excavated length of the wall, large
stone blocks had been laid at intervals on this platform. Iron retaining
rings, presumably for use with cannon, were found on either side of
each gun-port; these rings were embedded in blocks of masonry, which
were set into the brickwork. On one of these blocks a further banker
mark was found (Fig.3, j). A line of plaster 48 cm. below the top of the
wall indicated that there had been a floor at this level.
THE INTERNAL WALLS
During the course of the excavation a number of brick-built interior
walls were found, none of which appears on the 1715 plan mentioned
in the introduction, and must be of later construction.
Post 17 15, period III - wall 2
This wall is of substantial proportions being l · 10 m.-wide and 2·08 m.high;
brick-built in English bond, it seals off the D-front of the
blockhouse. It is assumed that this wall served as the outer retaining
wall of the building at a later period when the fortifications of the
Tudor wall had either become obsolete or ruined. A ledge 10 cm.wide
and 5 cm.-deep runs the entire length on either edge along the top
of this wall. There is also a central depression l · 12 m. in length and
5 cm.-deep along the complete width of the wall. This depression was
found to be filled with burnt material. A feature of this wall at its
junction with wall 1, shows this wall is not simply butted directly
against it, but the upper half is sprung by means of an arch so that only
the top portion is in contact (Fig. 4). Initially, it was assumed that this
method of construction was to accommodate the protruding platform
of wall 1. However, the arch technique was later found to be employed
elsewhere. The only explanation so far offered is that the later builders
did not trust the foundations of the earlier walls· and this could have
been a way of overcoming this problem.
157
D. THOMPSON AND MRS. V. SMITH
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k
Fig. 3. Mason's 'Banker' Marks.
158
EXCAVATION OF THE GRAVESEND BLOCKHOUSE, 1975-76
Wall
1
Wall 2
1
scale 25 th
Fig. 4. Detail of arched Construction.
1633-post-1715, periods II and III - wall 3
A survey for repairs was made in 1633, of which one item recorded was
the laying of a stone paved floor. Evidence for the carrying out of this
work was confinned by the discovery of a number of portions of
flagstone in situ around the inner perimeter of wall l . This floor had
been laid on a foundation of rubble and evidence exists to show it to
have extended over the entire internal area excavated. Wall 3 was built
onto this floor, it is only 25 cm.-wide and 73 cm.-high and runs parallel
to and abuts wall I for its entire length. Where it meets the radius of the
D-shaped front of the Tudor wall, the curve is eliminated by the
employment of a spliced joint. At the southern end, it crosses wall 6
(see below) using an arched construction similar to wall 2. This wall
was not merely a refacing of wall 1, but was built to support floor
joi_sts. Evidence to support this theory is shown by the top course of
brickwork being complete and having no trace of mortar, but traces of
a wooden beam were found overlaying this wall. A break of l ·20 m. at
one point in the flagstones, coupled with the fact that the wall extends
seeral courses lower between this gap, indicates that some feature
existed at this point; a row of bricks laid end-on built into the wall
centrally above this feature may have had some association (Fig. 5).
159
D. THOMPSON AND MRS. V. SMITH
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Fig. 5. Detail of Feature at Centre of Wall 3.
Post-1715, wall 4
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This wall, 2·25 m. from wall 3, runs at right angles to wall 2, to which it
is connected by a simple butt joint. It is of modest dimensions, being
only 46 cm.-wide and 98 cm.-deep. A foundation trench for this wall
had been cut through the rubble foundations of the flagstone fl9or.
This trench although filled with the same rubble as the general area was
discernible. At its south end where it crosses wall 6 the same method of
arched construction as in walls 2 and 3 was found to exist. Conclusions
concerning its function are identical to those made for wall 3.
Post-1715, wall 5
This wall is similar in construction and proportions and stands at riiht
angles to wall 2. Unfortunately, owing to the limits of the excavation
area, it was only possible to examine its west face, which bore no
significant features. An exploratory trench into the adjacent flower
beds was cut to ascertain its width, which proved to be 1-40 m., but
unlike wall 4, the joint with wall 2 had been securely keyed-in and 'is
undoubtedly contemporary.
Periods I and III, wall 6
The 1715 plan, which was the pattern on which the excavation was
based, showed an interior cross-wall approximately 12 m. south of the
extreme front of the building. This was successfully located, and it was
apparent by its construction that it had been rebuilt. However,
subsequent excavation showed that this rebuilding only applied to the
top seven courses of brickwork below which remained the original
Tudor work. At the junction of these two periods were further portions
of flagstone in situ. The brick platform of wall 1 was found to return
along this wall although its width was reduced to 28 cm. A stone block
laid on this part of the platform contained another banker mark
(Fig. 3, k).
160
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Fig. 7. Masonry Fragments.
EXCAVATION OF THE GRAVESEND BLOCKHOUSE, 1975-76
These six walls combine to divide the excavated area of the
blockhouse into three parts conveniently described in this report as
rooms 1, 2 and 3.
Room 1
This is the area delineated by the D-shaped exterior wall and the
cross-wall 2. The clearing of this area showed that the infill consisted of
brick and mortar rubble, below which the material although still predominantly
rubble contained an admixture of clay in which a number of
pieces of cut masonry were found (Figs. 6 and 7) indicating that
the laying of the flagstone floor was accompanied by other
considerable structural alterations. Below this second layer was found
a layer of crushed chalk into which the foundation trench for wall 2
had been cut. Removal of this layer showed it to be 70 cm.-thick and
overlay an extremely solid mass of clean chalk, which was later
confirmed as being the original raft upon which the whole structure
was built.
Room 2
The area of this room is contained by the cross-walls 2 and 6 and walls
3 and 4 which are at right angles to them, its dimensions being
2·30 m. x 6·50 m. The infill was found to be identical to that described
for room l, except that between the mixed rubble and clay layer and
the crushed chalk, an uneven layer of burning was discovered. Beneath
this burning, there was a deposit of clay into which three timber joists
appeared to have been laid (Fig. 6). This may have been the remains of
an early wooden floor as several dozen iron arrowheads were found at
this level. The two brick structures noted on the site plan were built
directly on to this burnt layer; they are of solid construction, 50 cm.
square, but their function has not been determined. The foundations of
wall 4 were also found at this level.
Room 3
The area designated room 3 is contained to the north by wall 2 and to
the east and west by walls 4 and 5. Although it was not possible to
excavate to the southern end, it is presumed to be bounded by wall 6.
The rubble infill of this area was superficially similar to that in rooms l
and 2. However, the mortar content appeared to be lighter in colour
and of a more powdery texture and, on analysis (see appendix), proved
to be of a completely different type. This infill penetrated down to the
chalk floor noted in rooms 1 and 2 with the exception of an area
163
I
0
D. THOMPSON AND MRS. V. SMITH
CLAY
metres
room 2
1
Fig. 8. Ground Plan, Room 2.
164
21
1
1
I
EXCAVATION OF THE GRAVESEND BLOCKHOUSE, 1975--76
adjacent to wall 4, where the layer of burning and its associated clay
layer extended under the foundations of wall 4 running out at varying
distances from 20-30 cm. into this area. No evidence was found for a
wooden floor over the remaining major portion of this room and, as it
is obvious that rooms 2 and 3 were originally one, the wooden floor
noted in room 2 may possibly have been merely a free standing
platform for storage or a walkway. The dissimilarity in infill material
between rooms 2 and 3 would indicate differences in periods of use, but
no dating evidence to prove this point was found, though room 3 must
have been in use at least until the construction of wall 4.
The foundations
To investigate the chalk raft on which the blockhouse was built, a
section was dug immediately in front of the exterior wall. This attempt
had to be abandoned due to enormous portions of fallen masonry
which would have required the use of heavy lifting tackle to remove. A
second attempt made outside the west of the building proved more
successful and the lowest courses of stone facing were found at l ·61 m.
below the offset. Below this, the brickwork extended for a further
61 cm. where it was found to be laid directly onto a compact mass of
chalk. An attempt to ascertain the depth of this chalk had to be
abandoned at a further 70 cm., owing to the instability of the trench
sides. However, a small trial hole was continued for a further 50 cm.,
but this still failed to establish the total depth of the chalk,
The old river wall
During the investigation of the foundations a timber structure was
found which has been identified as an earlier wall. It consisted of two
oak uprights, their dimensions being 18 x 16 cm. As excavation
proceeded, it was found that planks approximately 19 cm.-wide and
3 cm.-thick had been bolted horizontally to the landward side of these
uprights, which were ultimately discovered to be attached to a sleeper
beam laid into a slot cut into the chalk raft. Subsequent removal of the
cross members allowed the uprights to be withdrawn from the sleeper
beam, which showed the method of attachment; this consisted of a
mortise and tenon joint secured by large iron bolts. Although corroded
beyond recovery their diameter could be assessed as approximately
5 cm. by the size of the holes drilled through the timber to
accommodate them. Behind this timber structure a backfill of dark firm
clay, evenly interspersed with crushed chalk, was filled to the level of
the top of the offset of wall 1, which extended backward to the
sourthern limit of the excavation area. During the removal of this
165
D. THOMPSON AND MRS. V. SMITH
backfill, it was found to contain several longitudinal holes retaining the
imprint of wood· grain and pieces of decayed timber. One of these
holes, 15 cm. in diameter and over 2·40 m. long, runs parallel to the
outer wall and may indicate the site of a drain as one end extended to
the edge of the old river wall, and the other turned slightly inward
towards the blockhouse. It has not been possible to ascertain a date for
this backfill, but it cannot be contemporary with the original building
as a bricked-in feature associated with the vertical rise in the offset
noted in wall 1 was buried by this fill. The riverward side of the river
wall was filled by predominantly pure mortar and was possibly used as
a dump for waste from the cleaning of building materials at one stage
of reconstruction.
Discussion
Unfortunately, the area available for excavation allowed only partial
investigation of the blockhouse to be undertaken. However, sufficient
evidence was found to confirm the authenticity of the 1715 plan and to
establish its precise location. Throughout its long and varied history,
alternating between periods of decay and subsequent restoration
during times of crisis, a number of structural alterations, mentioned in
the text, had been carried out, but there is little evidence to show a
chronological sequence for these events, the only exception being the
1633 proposal for the laying of a stone floor and its foundations which
seal the lower layers - provided that the correlation of the
documentary evidence concerning this feature and the actual flagstone
floor found is accepted. A report of 1730 regarding the collapse of the
front wall of the building can be substantiated by the finding of a large
portion of wall fallen from the superstructure, which the stratification
shows to have been sealed before the general destruction level.
The completion of the excavation leaves problems which require
elucidation, one of which is the reason for the arched construction
employed in the post walls, another concerns the iron retaining rings
on either side of the gun-ports, which seem unusual at this early date.
However, the excavation is not to be completely backfilled, as the
owners requested this and intend to re-landscape the area and generally
keep the structure in good repair for viewing by the public.
ACKNOWLEDGEMENTS
We are indebted to the landowners, Messrs. Berni Inns Ltd., for
allowing us to excavate on their property; also, to the manager of the
Clarendon Royal Hotel, Mr. M. Hayden and his staff, for their cooperation.
166
EXCAVATION OF THE GRAVESEND BLOCKHOUSE, 1975-76
Our thanks are due to Mr. V. T. C. Smith, of the Kent Defence
Research Group, for inviting us to dig on their behalf and for
supplying us with a copy of the 1715 plan.
The excavation was carried out entirely by members of the
Thameside Archaeological Group, of whom the following deserve
special mention for their sustained efforts: Mrs. L. Peasey, Mrs. R.
Geer, Miss K. Mercer, Miss N. Egan, Messrs. R. Mills, F. Holder, K.
Morris, K. Webster, J. Dryden and P. Relf; and also Mr. B.
Fitzpatrick and Mr. L. Mercer, for surveying the site; Mrs. L. Smith
and Mrs V. Docksey, for drawing the small finds; Mr. E. Tilley, for
identifying the coins and the report on the clay pipes; Mr. J. Shepherd,
for the glass report; and, finally, our thanks are due to Mr. A. Swaine,
B.A., F.R.I.B.A., Mr. P. J. Tester, F.S.A., and Mr. F. W. Jessup,
C.B.E., M.A., LL.B., F.S.A., for their valued comments and
encouragement.
APPENDIX I
The Pottery
During the excavation only a small amount of pottery was found,
ranging from a survival sherd of thirteenth-century ware, several small
fragments of stone ware, two examples of Staffordshire ware and the
remainder datable to the Victorian and later periods. As they are all
from unstratified deposits no further mention need be made.
APPENDIX II
The Glass, by J. Shepherd
(Fig. 9)
Bottles (free-blown). Fragments of four free-blown bottles can be
identified
No. 1 Neck and rim, natural green nineteenth-century soft drinks
bottle.
No. 2 Neck and rim fragment, the surface completely corroded and
the glass looks opaque, but an amber-brown tint shows on a
recent fracture. Late-seventeenth-century wine bottle.
Fragments not detailed. Part of a cylindrical bodied bottle, pale green,
vrying in thickness from 6-10 mm. The fragment is completely coated
wth heavy iridescence. Late-seventeenth-early-eighteenth-century
wme bottle.
Fragment, pale green, part of a cylindrical bottle, thickness varies
from 2-4 mm. Eighteenth-century wine or beer bottle.
167
D. THOMPSON AND MRS. V. SMITH
Jn
1
2
3 I
. ·
-l Q-J a
Fig. 9. Glass Fragments (Scale: ½).
Vessels (mould-blown)
No. 3 Fragment, transparent blue glass with mould-bl@wn pattern,
possibly the side of a small square jar or bottle.
Nineteenth -twentieth century.
No. 4 Fragment, clear amber, blown in a two- or three-part mould,
regular pattern of raised blobs of same colour, a mould mark is
also visible. Nineteenth-twentieth century.
No. 5 Two adjoining fragments of colourless glass from an
unidentifiable vessel.
Wine Glass
No. 6 Stem and base fragment from a wine glass, colourless, ·but now
has a fine iridescent coating. The angular knop-and-cushion
stem formation is a close approach to one of John Green's
patterns of 1660 to 1680. He was a London glass importo/ wh?
corresponded with a Venetian glass maker, Alessio Morelli.
Letters and drawings of glasses ordered are preserved in the
British Museum.
Window Glass
Eight fragments of window glass can be divided into two
groups:
(a) Three fragments, 1·5 mm.-thick, colourless, cylinder sheet
process and not manufactured until 1832.
168
EXCAVATION OF THE GRAVESEND BLOCKHOUSE, 1975-76
(b) Five fragments, I mm.-thick, pale green, but now brown
with corrosion. The fragments come from a diamond
pattern leaded lights and date before group (a).
APPENDIX III
The Round-shot and Arrowheads
During the excavation of the lower rubble fill of room 2, a number of
round-shot was found. The first had a diameter of 6· 3 cm. and is
consistent with that of a projectile intended to be fired by a gun called a
falcon. The falcon had an extreme range of 1,300-1,500 yards. As a
gun-type, it was in use in England through the entire period when guns
were mounted in the biockhouse itself. Falcons were in the original
armament and were definitely present as late as 1600.
Six other shot were also found having a diameter of 5· l cm. and may
have been fired from a weapon called a falconet. The falconet was a
slender, almost fragile looking, gun which was used in the sixteenth and
seventeenth centuries, although this gun is not listed in any armament
list yet found for the blockhouse. (We are grateful to Mr. V. T. C.
Smith, for the above information.)
On the remains of the wooden floor of room 2 were discovered
several small iron objects resembling arrowheads, which were later
identified at the Tower of London as being the tips of cross-bow bolts.
APPENDIX IV
Coins and Clay Pipes, E.W. Tilley
Coins
I. Unstratified.
Chinese brass 'cash' of the Ch'ing or Monchee dynasty c. 1780
Emperor Kien Lung, 1736-1796. Mint illegible.
2. From the rubble filling of room 2.
Dutch copper 'Doet' of the province of Holland c. 1758
obverse - Lion within a fence
reverse - HOL/LAN/DIA and date below
N.B. The Dutch provinces all struck copper Doets bearing the arms
as the obverse and the name of the province on the reverse.
169
D. THOMPSON AND MRS. V. SMITH
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