trench

A trench is a long, narrow depression in the earth or seabed. It can be a man-made channel for drainage, irrigation, utilities, or construction, or a natural feature formed by geological processes such as subduction at tectonic plate boundaries or erosion along a watercourse. In military contexts, trenches are earthworks dug to provide cover, concealment, and defensive positions.

In warfare, trenches are typically long, interconnected ditches with various features such as front-line sections, support lines, and reserve lines, often connected by communication trenches. They may include parados (back walls), duck boards to keep feet above mud, fire steps for firing from a standing position, and dugouts for shelter. Trench warfare became a defining characteristic of World War I, with brutal conditions, including mud, water, vermin, and disease, shaping tactics and the experience of soldiers.

In civil engineering and urban construction, trenches are excavated channels for laying pipelines, utilities, or drainage systems. Works require shoring or trench boxes to prevent collapse, as well as safe access and egress, dust and vibration controls, and careful management of spoil and utilities to minimize disruption to surrounding areas.

In archaeology and field science, trenching is a controlled digging method used to sample subsurface layers, establish stratigraphy, and recover artifacts. Evaluation or test trenches help researchers assess sites before larger excavations.

Geologically, trenches also occur as natural depressions, most notably ocean trenches such as the Mariana Trench, formed where one tectonic plate dives beneath another. These deep features are key to understanding plate tectonics and Earth's upper mantle.