Shornemead Fort is a now-disused artillery fort that was built in the 1860s to guard the entrance to the Thames from seaborne attack. Constructed during a period of tension with France, it stands on the south bank of the river at a point where the Thames curves sharply north and west, giving the fort long views up and downriver in both directions. It was the third fort constructed on the site since the 18th century, but its location on marshy ground led to major problems with subsidence. The fort was equipped for a time with a variety of large-calibre artillery guns which were intended to support two other nearby Thamesside forts. However, the extent of the subsidence meant that it became unsafe for the guns to be fired and the fort was disarmed by the early 20th century.