The Danelaw (from the Old English Dena lagu, Danish: Danelagen ) is an 11th-century name for an area of northern and eastern England. This area was under the administrative control of the Danish Viking empire (or Danes, or Norsemen) from the late 9th century until the early 11th century.
As can be seen from the map, Danelaw at its height was about a third the territory of England. Textbooks say correctly that the history left us with place-names which reflect the old languages.
- K. Holman, The Northern Conquest: Vikings in Britain and Ireland, p. 157
- S. Thomason, T. Kaufman, Language contact, creolisation and genetic linguistics, p. 362
- The Blackwell Encyclopedia of Anglo-Saxon England, ed. Michael Lapidge (2008), p. 136
- The place-name term to look for is "toponymy" or "toponymics", and English wiki has a page on Place name origins.