A trench is a long depression in the ground which is deeper than it is wide, with a width which is significantly smaller than its length. Trenches may be constructed artificially for a variety of purposes, and they also occur naturally. Essentially, a trench is an oversized ditch, with some trenches having some extra features.
In nature, trenches are most abundant in the ocean, where they are known as ocean trenches. Ocean trenches are formed by the buckling, folding, and spreading of the sea floor, and some of them can get extremely deep. In the case of abyssal trenches like the Mariana Trench, ocean trenches can also sometimes harbor interesting and distinctive animals. Natural trenches on land are formed through a variety of process, in some cases eroding and expanding to turn into valleys and other large natural features.
Humans have been constructing trenches for a variety of purposes for thousands of years. One of the earliest uses of the trench is in fortifications for warfare, as investigations at some archaeological sites have revealed. Trenches have also been utilized in agriculture to transport water for irrigation. Trenches continue to be used for these purposes in many regions of the world. Trenches are also used to make fencing and dividing lines between fields.
Trenches are also sunk for the purpose of installing utilities. Keeping gas, electric, and phone lines underground reduces clutter aboveground, with the earth acting as natural insulation. Utility workers may also sink search trenches to determine the location of utility lines if they aren't exactly sure about where to look. Road workers often sink search trenches to determine the precise location of underground utilities, which is why they periodically tear up chunks of the road, spray paint obscure markings, and then replace the sections again.
Archaeologists also utilize trenches in their work. In order to investigate sites in an orderly way, archaeological teams start by sinking a series of shallow trenches, and then work their way slowly down, sifting the soil as they go to look for artifacts. Creating archaeological trenches can be a painstaking process, as the goal is to preserve the site as much as possible while uncovering it and taking notes on the locations where artifacts are found. Many archaeological sites bear the evidence of multiple civilizations which simply built on top of each other, making it critical to keep the layers of a site separate so that the provenance of artifacts is not confused.