• "Benchmarking Medieval Economic Development: England, Wales, Scotland, and Ireland, c.1290":
https://www.jstor.org/stable/40057660

• "S2 Appendix: Database Construction":
https://www.researchgate.net/publication/309510929_S2_Appendix

• "European urban population, 700 - 2000":
https://ssh.datastations.nl/dataset.xhtml?persistentId=doi:10.17026/dans-xzy-u62q