Ditch

A common feature of archaeological sites in association with defensive structures, as a means of drainage, or as a construction trench. A ditch was usually dug outside the walls of forts, fortresses and so on, as part of the defenses, and was often filled with water. Ditches which are allowed to erode, without much interference, go through three phases of infilling. Primary fill accumulates as the sides of the ditch collapse. Vegetation then begins at the bottom of the ditch and the secondary fill starts to build up. This material has a much finer texture than primary fill. The rate of secondary fill deposition is related to soil erosion in the surrounding area. If the land by the ditch is plowed, thick colluvial deposits, called tertiary fill, may bury the secondary fill.

A common feature of archaeological sites, not only as defensive structures in association with ramparts and walls, but also as a means of drainage or as a construction trench. Large ditches which are allowed to erode, without much interference from man, go through three phases of infilling. Primary fill accumulates rapidly as the sides of the ditch collapse. When the sides reach their angle of rest, the rate of deposition slows down, vegetation colonizes the bottom of the ditch and the secondary fill starts to build up. This material has a much finer texture than primary fill; it accumulates by in wash and from windborne particles trapped in the ditch bottom vegetation, and is subject to soiL-forming processes. The rate of secondary fill deposition is related to soil erosion in the surrounding area. Finally, if the land adjacent to the ditch is being ploughed, thick colluvial deposits, called tertiary fill, may bury the secondary fill. This sequence may be interrupted by tippingin of additional material by man. The smaller drainage ditches within a site tend to be filled by the tipping of rubbish and similar material rather than by the sequence of fills seen in larger ditches. Experimental archaeology has shown that as a result of erosion the excavated profile of the ditch may bear little relation to the original form, and that layers within the fill of a ditch may be more related to erosion and soil-forming processes than to human activity.