A defensive structure is a type of structure that is designed to protect an area from attack. RAMPART, which has seven letters, is a type of defensive structure that is made up of an earthen embankment with a wooden PALISADE on top. FORTRESS, which has eight letters, is a type of defensive structure that is usually made of stone or brick and is designed to withstand attack. PALISADE, which also has eight letters, is a type of defensive structure that is made up of a fence of wooden stakes or posts.