The earthwork remains of three large irregular mounds thought to be medieval saltern mounds. These mounds form part of a cluster of similar mounds extending along and a water-filled creek in the marshes which have been mapped from aerial photographs as part of the English Heritage: Hoo Peninsula Landscape Project. These mounds are the result of large-scale salt manufacturing where brine was extracted from salt-rich sands and sediments, concentrated and evaporated using process known as sleeching. The discarded waste material from the process built up around the production area into a sizeable mound, often with a hollow in the centred where a hut stood. These medieval saltern mounds are typically described as `floriate' in form because of their irregular lobed formation of dumped waste. They often occur in clusters around former and surviving tidal water-courses within the marsh. There has been considerable reclamation and subsequent sea wall construction since the medieval period which has isolated these sites from the sea. Many of these mounds were subsequently utilised as sheepfolds, sheep washes and stock refuges in the post medieval period because of their slightly elevated position in the readily flooded marshes. In common with many such sites, finds of 2nd century Romano-British pottery have also been found adjacent to these three mounds. However, generally such finds are believed to be from the lower levels, and not associated with the mounds. Post-Roman flooding and silt deposition has resulted in Roman sites lying typically several feet below the current land surface.