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The Royal Military Canal was constructed between 1804 and 1809 as a defensive structure to help protect southern England from invasion during the Napoleonic Wars. Martello Towers were created for the same purpose at the same time, as the threat from Napoleon was considered very real and worth the vast expenditure that was required for these various defences - £234,310 for the R M Canal alone for example, equivalent to many millions today.
The canal runs for approximately 28 miles along the border of the Romney Marsh, with all but 5½ miles of this having to be dug. Its most easterly point is at Seabrook in Kent where construction commenced on 30th October 1804. It was only supposed to take just over a year - and although the first section to the River Rother was open by 1806 it was not finally fully opened until April 1809 - by which time the threat from Napoleon had gone away and the State was left with a costly "White Elephant", but one which with time has become a much loved feature of this part of England.
For much more detail on all aspects of the RMC, visit its own website Link

The Royal Military Canal stretches for 28 miles hugging the old cliff line that borders the Romney Marsh from Hythe in the north east to Cliff End in the south west. It was built as a third line of defence against Napoleon, after the British Royal Navy patrolling the English Channel and the line of 74 Martello Towers built along the south coast. The Royal Military Canal was constructed in two sections. The longest section starts at Hythe in Kent and ends at Iden Lock in East Sussex. The second smaller section runs from the foot of Winchelsea Hill to Cliff End. Both sections are linked by the Rivers Rother and Brede.

See Link and Link for more details