This ancient earthwork ditch – built about nine-feet-wide with a shallow ditch either side – runs intermittently from the Flosh Burn, near Robert’s Linn bridge, to Hoscoteshiel, near Girnwood farm on the Borthwick.
Earthwork boundaries were, and always have been a common way of delineating the land belonging to a settlement or farm, but given the comparatively lengthy twelve-mile stretch of the Catrail, it is widely accepted to be part of the boundary of a far larger unit of land. It seems likely, in fact, that it would once have separated the Kingdom of Bernicia (6th-7th century Anglo-Saxon kingdom comprising modern-day northeast England and southeast Scotland) and their native neighbours to the southwest, the Britons. (Note that the Catrail runs in a distinct northwest-southeast direction.)
At many points along its route, the earthwork of the Catrail is replaced by the natural boundary lines of rivers and streams. Today, few parts of the earthwork greater than six feet in width, and half a metre in height, can be discerned.