Offa's off?

[Sharur]

There's also the Roman Ridge (sometimes "Rig") Dyke (sometimes "Dykes") between, very approximately, Sheffield and Doncaster in southern Yorkshire, apparently designed for defence against the south, and although modernly typically supposed as having been constructed by the Brigantes in Roman times, has also been suggested as covering part of the southern border of Northumbria at some point in maybe the 7th-9th centuries. It's undated. About the best descriptive source I've found online for it so far is here:

http://www.brigantesnation.com/SiteResearch/Iron%20Age/RomanRig/RomanRig.htm ,

though this barely mentions the early medieval option.

The Bar Dyke on Broomhead Moor is nearby as well (similarly undated, with suggested construction dates guessed-at from the Bronze Age to the 7th century AD), which might be related. This site has some brief notes and a few photos of it:

http://www.themodernantiquarian.com/site/2698/bar_dyke.html .

[Jim Webster]

There are mixtures of banks and enclosures in various parts of England that are assumed to be for cattle handling
Jim

[Imperial Dave]

I wonder if, for perfectly comprehensible reasons, we leap to military explanations. It is just as possible that this represents an agreed boundary between two post Roman states. Do we have evidence that there were garrisons along the dike? 
Roy

I'd always thought the consensus was a boundary between two states rather than an early medieval Hadrian's Wall.  While it is possible it is lots of little boundaries later connected together, as suggested, it seems at least possible it is part of one political settlement over a wider area.

seems emminently reasonable to me. Walls/dykes/fortifications are always a way of slowing down traffic through a frontier area. We dont have to assume military in this instance. Interestingly there has been evidence for high status continuity at the Wrekin in Shropshire into the 6thC which is in the right ballpark area as this section of the Dyke............