Is the Barrow a European Thing? Mapping and Dating Europe's Burial Mounds

Burial mounds and burial cairns are found from Ireland to the Pontic steppe, but are they a European tradition, or a north-west European one? I assemble 99,049 European barrows from OpenStreetMap and Wikidata, remove duplicates, assign types and periods, and measure density by country and by 50 km square. Raw counts lean strongly north: 83% of barrows lie north of 50° N, on 62% of Europe's land. But 92% of the records come from eight countries whose national or regional heritage registers were imported in bulk, covering 20% of the land; outside them, the northern lean disappears (41% north of 50° N on 61% of the land). A ratio that cancels most mapping effort, mounds as a share of mapped mounds and megaliths, shows a robust contrast between a stone-built Atlantic edge (France 5%) and an earthen lowland belt from the North Sea to the Black Sea (Poland 95%, Ukraine 100%). Linking 489 radiocarbon dates from 132 sites named as barrows in the p3k14c database and calibrating them with IntCal20, 33% of site-weighted dates fall before 2500 BC and 59% between 2500 and 800 BC; long barrows have a median date of 3640 BC. The steppe is too thinly recorded to test whether it is a second heartland. The barrow is a European tradition with a Bronze Age peak; its apparent north-western heartland is in large part a heartland of records. Interactive version: https://tristan-hotham.github.io/barrows-of-europe/. Data and code: https://github.com/Tristan-Hotham/barrows-of-europe. Blog post: https://blog.tristanhotham.com/2026/10/27/barrows-of-europe/.