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A historic military site on the north bank of the Thames estuary opposite Gravesend, developed mainly in the time of the Spanish naval threat of the 17th century with massive low earthworks to resist artillery bombardment. It continued in use intermittently until World War 2, with further developments reflecting the development of naval or aerial warfare in each conflict.

It is now listed as a Scheduled Ancient Monument and operated as a historic tourist attraction by English Heritage.

This route will connect Tower Bridge in London with Fakenham in Norwich. Passing through East London close to the Thames, Route 13 then heads north from Tilbury to Chelmsford in Essex. After a stretch on National Route 1 (also part of EuroVelo 2) National Route 13 resumes at Colchester and continues north to rejoin National Route 1 just south of Fakenham in Norfolk.
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