Wansdyke is a ditch and embankment defensive structure running east-west through Somerset and Withshire. It was constructed at the time of, or following, the Roman evacuation of Briton around 500ad..
There are three theories about who it was defending. The most popular is that it was constructed to defend Britons from the westward encroachment of the recently arrived Saxons. I quote Trevor Rickard:
This theory is supported by the 9th centuryHistoria Brittonum, and specifically its narrative of the Battle of Mons Badonicus. In this battle the native Britons, supposedly led by King Arthur himself, hit a decisive blow against the Anglo-Saxons and prevented them from gaining any more land for at least the next 50 years.
It is not known where the Battle of Mons Badonicus took place but it is at this time that Briton territory and Saxon territory adjoined in Wiltshire and Somerset. It is believed that Wansdyke was constructed as a defensive line on this frontier.
The other theories are that it was a Roman construction as Roman coins have been found in the location dating from this period, or constructed by the Saxons against incursions from the Britons.
Ordnance survey maps show Wansdyke with remnants beyond Lockeridge, pictured here, it is by the further lodge of Shaw House. It also runs through West Woods and can be found near Cadley by taking the overgrown bridlepath from the A346. The ditch and embankment are clearly discernable although much reduced.
Further information can be found on the internet under ‘Wansdyke’ on the UK Historic site.