Docklands History Group Meeting – Wednesday 7th October
Roman Walbrook and its Legacy
By Tony Taylor
Tony explained that he was a civil engineer who had worked with archaeologists, on sites in the City
of London, since 1984.
The Walbrook could be classed as a lost river, although it still existed underground. It was recorded
by John Stowe in his 1598 Survey of London as flowing through the City into the Thames.
The course of the river Thames through London meanders in a wide valley some 2km wide. By
Roman times that course had meandered over the previous 10,000 years from south to north in the
city area some two kilometres and had left eyots on the low lying south side, due to erosion of the
gravel terraces by the river. This meandering further north was cutting into Cornhill and Ludgate
Hill. Due to the changes, the rivers to the north of the Thames got shorter and the Fleet and the
Walbrook lost 2 km of their length. In addition the sea level during the Iron Age had risen by six
metres resulting also in a three metre tidal variation in the City area.
From Tony’s research of boreholes at Cannon Street into the river bed of the Thames he had a low
tide depth of approx. 1,2m. Given this Tony believed the bed of the river being composed of gravel; it
had been possible, using the eyots, to ford the Thames between the Walbrook and the Wapping
Stream onto Cornhill. Caesar and his army it was reported crossed the Thames up to their necks in
water. When the Romans returned they would have known Caesar had managed to cross the Thames
at this point and so it was suggested by Tony that this was why they commenced building on Cornhill.
Boudicca destroyed the settlement, but the Romans rebuilt it and expanded it and built the first
London Bridge across the Thames.
A map of the Walbrook prepared by Tony showed the Walbrook served forty percent of the
catchment area of Roman London. It rose in Islington, which had gravel terraces and was at a height
of 35 metres above chart datum and then flowed down as a series of fast flowing streams coming
together in the flat area of Hackney. It then flowed into the City cutting down a valley creating
Cornhill and Ludgate Hill. To help research the catchment area Tony had used Victorian maps as it
was not until the 19 century that the first maps with accurate levels were produced. The surface
deposits of clay and brick-earth were too variable for comparison; however, the gravel was a constant
formation to map the underlying contours to demonstrate to archaeologists where to look for the river
course.
At Broadgate in 1984 an East West trench archaeological excavation had revealed the original natural
Walbrook stream. A Roman levee measuring 20 sq. metres or some 40 tons per metre of brick earth,
had been uncovered running north, probably to control flash flooding. 1.25 metres of peat had built
up into a bog, over one thousand years, having been deposited Tony believed between 250/300 AD
and 13/1400 AD. The Romans had built the City wall across the Walbrook which then flowed
through a culvert under the wall which was found in 1836 when a new sewer was being installed. It
had an arch of tile and stone around it and a road along the inside of the wall above. The water would
only be able to flow at one cubic metre per second through the culvert which was a severe constraint
such that in winter there must have been a build up of water behind the wall and this flood created the
area of peat and what we now know as Moorfields.
In 1250 Bethlehem Hospital was built alongside the deep ditch (the Walbrook) in the location close to
the Broadgate trench The City wall diverted the stream eastwards around the city wall along what we
now call Houndsditch, which was fed by the Walbrook.
Tony said he had his own theory of where the Walbrook ran, following the natural contours of the
land. The street system in the City was based on the landscape. He believed the Walbrook ran from
west of Broad Street down to Draper’s Gardens, with three tributaries on the west side. There was a
burial ground adjoining which might explain the skulls found in the Walbrook, as they travelled more
easily in water. He thought it possible the Romans had created diversions capturing other tributaries
to increase the Walbrook’s flows.
At Draper’s Gardens a Siefert Tower was built on a raft and around it in the shallow basement Roman
deposits had been found. On the south side a Corduroy structure had been found which was thought
to be a track/boundary. Many revetted channels were discovered in phases stretching from the late 1st
to the 5th Century across the site. It was logical to assume that these may have received water diverted
from the Walbrook. Over decades of time there would, have been a flash floods, such that up to 20
tons of water per second passing down the Walbrook. Tony speculated that between 75-8 AD when
Julius Sextus Frontinus was Roman Governor, he drew up a masterplan for the Walbrook waters in
terms of structure and a network of channels with sluices, possibly for milling. On his return to Rome
he took charge of water and sewage there. Unfortunately at Drapers much of the evidence was
hidden by city streets which could not be excavated.
The Roman oak boarding revetments found were constructed by driving in timber piles and then
attaching the side revetted boards. The waterlogged ground preserved Roman timber floors and a
whole Roman door, cored logs forming a water pipe with iron connecting tubes driven into their ends
and a bend at the end formed by a lead shoe had been found.
At Bucklersbury in 1952 excavating a bomb site, Professor Grimes dug trenches East to West across
the site and found a Roman temple and head of Mithras. After a clamour from the Public at that time
the temple was dug up and later rebuilt (badly) on a podium accessible from Queen Victoria Street.
Today the site is once again subject to development and the Temple remains have once again been
removed and will be reconstructed next year in a purpose built space in the sub-basement area of the
site aligned and at the same level as the Roman original.
The natural valley of the Walbrook today lies some eleven metres below ground of which the
Romans alone had filled in 3.8 or more of those metres. The major raising of the ground had only
occurred primarily in the valleys and was probably designed for flood control. The Romans had
docks and had built walkways along the river and boats were able to navigate 200 metres up with the
tide. A large number of finds have been discovered on the Bucklersbury site and some water
structures which may be related to the Langbourn to the east of the Walbrook, on Cornhill. Tony
added that he had not researched this in any depth so far. At the Bucklersbury site Roman ink writing
had been found on timber, a leather shoe and a woven basket. The lack of oxygen meant that
oxidation could not start so objects were preserved in the saturated ground.
He then went on to talk of the Gresham Street Roman well and the bucket chain which had been
found and recreated. Vitruvius writing in 25 BC had described such a well. Here the Romans had
excavated the well some 4.5 metres below the water level and it was constructed as a 3.6 metre
square. It was lined with oak boards which allowed the water to enter under boards using the gravel
as a filter to give pure clear water. Many Victorian buildings subsequently used groundwater filtered
by the gravel terraces.
Finally Tony said that the Draper’s site post excavation report was still awaited. The Walbrook had
not been located at this site as it would have been deeper than the excavation went. The water level
had been below semi-basement level for hundreds of years now. Then Tony ran through again those
areas of the City which the Walbrook had influenced giving the legacy we have today
S. Mashiter and Tony Taylor
26.10.2015