(in Latin)(in Dutch) C.J.C. Broer and M.W.J. de Bruijn, Bonifatius en de Utrechtse kerk, in: C. Dekker and E.S.C. Erkelens-Buttinger (1997), De kerk en de Nederlanden, page 63, Verloren, ISBN90-6550-558-X
(in Latin) Alcuin, Vita Sancti Willibrordi, circa 795, chapter 14 (English translation)
handle.net
hdl.handle.net
Louwe Kooijmans, L. P. (1974), The Rhine/Meuse Delta. Four studies on its prehistoric occupation and Holocene geology (PhD Dissertation), Leiden: Leiden University Press, hdl:1887/2787
jaarboekvoormuntenpenningkunde.nl
Grierson, Philip (1973–1974), "Korte Bijdragen: A New Audulfus Frisia Triens", Jaarboek voor Munt- en Penningkunde(PDF), vol. 60/61, Amsterdam: Koninklijk Nederlands Genootschap voor Munt- en Penningkunde, pp. 153–156.
Halbertsma, Herrius (1982). "Summary"(PDF). Frieslands Oudheid (Thesis) (in Dutch and English). Groningen: Rijksuniversiteit Groningen. pp. 791–798. OCLC746889526.
unibg.it
aisberg.unibg.it
Zocco 2007, p. 67, "in the most generally accepted reconstruction the first assault is from the part of the Frisians in a treacherous onslaught which excites the Danish strenuous defence". The term Frisian side avoids imputing specific responsibility to either Finn, Frisians, Jutes, or others. Zocco, Nicola (2007), "The Episode of Finn in Beowulf. Discharging Hengest"(PDF), Linguistica e Filologia, 24: 65–83
One or more of the preceding sentences incorporates text from a publication now in the public domain: Lins, Joseph (1912). "Archdiocese of Utrecht". In Herbermann, Charles (ed.). Catholic Encyclopedia. Vol. 15. New York: Robert Appleton Company.
One or more of the preceding sentences incorporates text from a publication now in the public domain: Mershman, Francis (1912). "St. Willibrord". In Herbermann, Charles (ed.). Catholic Encyclopedia. Vol. 15. New York: Robert Appleton Company.
worldcat.org
Homans describes Frisian social institutions, based on the summary by Siebs, Benno E. (1933). Grundlagen und Aufbau der altfriesischen Verfassung. Untersuchungen zur deutschen staats- und Rechtsgeschichte (in German). Vol. 144. Breslau: Marcus. OCLC604057407. Siebs' synthesis was extrapolated from survivals detected in later medieval documents.[15]