What is a linear earthwork (dyke)?

What a linear earthwork (dyke) is

Prehistoric linear earthworks range from a few tens of metres to more than 80 kilometres long; they date mainly from the Middle Bronze Age and through the Iron Age, and are thought to have marked out land held by different communities. Cross dykes are shorter examples, usually between 200 metres and 1 kilometre long, built across ridges and spurs; Historic England dates them from the Middle Bronze Age onwards. Offa's Dyke, traditionally attributed to Offa, king of Mercia from 757 to 796, has a ditch on its western, Welsh side and a bank up to about 2.5 metres high; radiocarbon dates from some sections are earlier and are debated. Other dykes thought to be early medieval include Wat's Dyke and Wansdyke.

How linear earthwork (dyke)s look on LiDAR

A linear earthwork shows as a long bank with a parallel ditch, running for long distances across fields and woods, often ending at a steep slope or valley. A local relief model shows ploughed-down stretches where the bank survives only a few tens of centimetres high, and sky-view factor shows the ditch even where the bank has gone; the side on which the ditch lies is often used to judge which way the boundary faced. Hillshade shows large dykes well but loses lengths that run parallel to the light.

See LiDAR visualisations explained for what each method shows.

What can look like one

Park pales, woodland boundary banks, parish and estate boundary banks, hedge banks, hollow ways, canals, leats and disused railway earthworks can all look like linear earthworks. Park pales and woodland banks usually enclose an area, while a dyke runs across country.

Protection

Many stretches of linear earthwork, including surviving sections of Offa's Dyke, are scheduled monuments, protected in England by the Ancient Monuments and Archaeological Areas Act 1979 and in Wales by the Historic Environment (Wales) Act 2023.

Examples on the LiDAR

Where they are

Counties with the most linear earthwork (dyke)s that have a page here.

More examples