Britain in AD 500: What the Ground Tells Us. Mapping Early Medieval Evidence and Uncertain Kingdoms in Britain and Ireland from Open Data

Popular maps of Britain around AD 500 show a patchwork of kingdoms with firm borders, yet most of those names are first written down centuries later. I build an evidence-led alternative from open data: the Atlas of Hillforts of Britain and Ireland, Wikidata, Ireland's Sites and Monuments Record, Pleiades and Wikipedia. The resulting map places 891 pieces of early medieval evidence, with 397 Roman towns and forts as context, and shows 24 named kingdoms only as approximate zones with their earliest written mentions. Just 87 of 4,147 Atlas hillforts (2.1%) have dating evidence for AD 400 to 800; they are more often coastal (39% against 18%) and more often promontory forts (45% against 30%) than hillforts in general. In Great Britain south of the Forth, Anglo-Saxon cemeteries and settlements have a median longitude of 0.05 degrees west and Latin-inscribed stones and western high-status sites 4.09 degrees west; only 1 of 143 western sites lies within 50 km of an Anglo-Saxon site, and smoothed density surfaces of the two do not overlap. 97% of 402 ogham find-spots are in Ireland, and 92% of 139 inscribed stones are in Wales. These are patterns in two burial and commemoration habits recorded unevenly by national heritage systems, not maps of peoples. The interactive version and all data and code are openly available. Interactive version: https://tristan-hotham.github.io/britain-500/. Data and code: https://github.com/Tristan-Hotham/britain-500. Blog post: https://blog.tristanhotham.com/2026/10/28/britain-500/.