A cross-dyke is a substantial linear earthwork, typically between 0.20 and 1km long comprising one or more ditches arranged beside and parallel to one or more banks, which runs across an upland ridge or across the neck of a spur. Single banks and ditches generally have a narrow flat bottomed ditch while multiple examples have a ditch which is a V-shaped in cross-section. Cross-dykes are recognised as earthworks or as cropmarks on aerial photographs, or as a combination of both. Other components which may be present are trackways at the end or ends of the dykes.
Construction of cross-dykes, as revealed by excavation and by anology with associated monuments, appears to span a millenium from the Middle Bronze Age, though they may have been reused later. Superficially similar dykes may have been built for widely different reasons. Current interpretation prefers their use as territorial limits, and/or as internal boundaries and land allotment within communities, although they were once seen rather as trackways, cattle droveways or defensive earthworks.
Some of the dykes appear to have continued in use, or have had a secondary function as boundaries through medieval into modern times, judging from their close relationship to current and previous parish boundaries. The tradition of cross-dyke building therefore lasts from the middle Bronze Age to the beginning of the Roman period, perhaps with reuse and perhaps limited construction in medieval times.