The earthwork remains of three possible medieval saltern mounds can be seen on aerial photographs taken in 1947. This group is situated near the sea defences south east of Egypt Bay. There is a depression in the central and southern mound and these are thought to mark the site of original buildings. The northern mound includes a rectangular pond, possible reusing a depression similar to those seen in the other two mounds. This pond is depicted on the 1872 Ordnance Survey map. The mound represent the discarded waste material from salt manufacture, a process - known as sleeching - in which brine was extracted from salt-rich sands and sediments, concentrated and evaporated. Sites such as this could no longer operate once sea walls were constructed resulting in the conversion of an area from salt to fresh marsh. These were mapped from aerial photographs as part of the English Heritage: Hoo Peninsula Landscape Project.