Deep ditches are large, deep TRENCHES or moats that are dug into the ground. They are often used to protect a certain area from intruders or to provide a barrier between two areas. TRENCHES are typically long and narrow, while moats are wider and deeper. Both are usually filled with water, making them difficult to cross. Deep ditches have been used for centuries as a form of defense, and are still used today in some parts of the world.