Moat
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A moat is a deep, broad ditch, either dry or filled with water, that is dug and surrounds a castle, fortification, building, or town, historically to provide it with a preliminary line of defence. In some places moats evolved into more extensive water defences, including natural or artificial lakes, dams and sluices. In older fortifications, such as hillforts, they are usually referred to simply as ditches, although the function is similar. In later periods, moats or water defences may be largely ornamental. They could also act as a sewer.
The moat surrounding Matsumoto Castle
North view of the fortress of Buhen in Ancient Egypt.
A medieval moat castle in Steinfurt, Germany
The 17th-century fortified town of Naarden, Netherlands, showing bastions projecting into the wet moat
Trench
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A trench is a type of excavation or depression in the ground that is generally deeper than it is wide, and narrow compared with its length.
Depiction of the topography of the Puerto Rico Trench, the deepest part of the Atlantic Ocean
Automated trench digging on a street in Baku
Allied troops entrenched in the Battle of Tuyutí.