The last ditch defence for London from invasion by Napoleon was, appropriately, if optimistically enough, a ditch. The Royal Military Canal, to give this rather grand ditch its rather grand title, runs for 28 miles from Seabrook (near Folkestone) to Cliff End (near Hastings). It was never tested against France’s Grande Armée, but did have some uses in taming the wild, smuggler’s paradise of the Romney Marshes.
At the start of the nineteenth century, Britain faced the prospect of invasion by France. Napoleon had set his sights on the island kingdom and, with only perfidious Albion resisting the Europe-wide Napoleonic system, it seemed likely that invasion would come sooner rather than later.
“All my thoughts are directed towards England. I want only for a favourable wind to plant the Imperial Eagle on the Tower of London.”
The state and people were roused to fortify, arm and defend Britain on a scale never before seen. The south coast bristled with a series of fortifications and batteries and a huge proportion of the male population was brought into military service in to the regular army and navy and a series of reserve, militia and volunteer brigades.
The fortifications included the construction of a chain of ‘Martello towers’, concentrated in the south of England but also erected around Britain and throughout her Empire. The strength of these buildings is testified by the fact that nearly half survive and several were brought back into service as sites for anti-aircraft batteries in the Second World War.
On quite a different scale to the Martello towers was the Dover Western Heights fortress, a vast citadel and associated defensive structures designed to protect Dover and the rest of England from sea and land attack. Covering 33 acres and connected with the town’s other defences (including Dover Castle), it was a formidable undertaking covering an area almost three times larger than the entire fortress at the Tower of London.
This brings us to the point of this article and the final component of the south of England’s defence works – the Royal Military Canal and Road. Running for 28 miles from Seabrook (near Folkestone) to Cliff End (near Hastings), it is the UK’s third longest defensive monument – exceeded only by Hadrian’s Wall and Offa’s Dyke.
The canal was designed to help defend Romney Marsh, a vast, low-lying stretch of the coast which was particularly susceptible to a French landing. The Marsh had been left undefended on the grounds that it could be flooded if enemy forces were sighted. With the spectre of a French landing becoming a reality, this complacent notion was challenged.
The canal, known locally as Mr Pitt’s Ditch after the Prime Minister who had championed its creation, was to be 19 metres wide at the surface, 13.5 metres wide at the bottom and 3 metres deep. That is, until cost pressures caused the canal’s dimensions to be severely curbed – it is only half as deep in many places.
Excavated soil from the canal’s construction was piled on the north bank to create a wall, behind which troops could be positioned and moved out of sight of the enemy. The canal also featured distinctive ‘kinks’ in the design, allowing soldiers to fire along the straight lengths of the canal, if the enemy attempted to cross it.
It was never needed for its intended purpose, either from Napoleon’s troops or any future German invasion. It had cost a huge amount of money to build, £234,310 in 1808 prices (equivalent to a labour cost today of £184.9 million or an economic cost of £880 million, the latter roughly comparable to the cost of building and refurbishing the East London Line extension).
William Cobbett voiced typical criticisms of the works:
‘Here is a canal made for the length of thirty miles to keep out the French; for those armies who had so often crossed the Rhine and the Danube were to be kept back by a canal thirty feet wide at most!’