Trinoda necessitas ("three-knotted obligation" [1] in Latin) is a term used to refer to a "threefold tax" in Anglo-Saxon times.
Subjects of an Anglo-Saxon king were required to yield three services: bridge-bote (repairing bridges and roads), burgh-bote (building and maintaining fortifications), and fyrd-bote (serving in the militia, known as the fyrd).
[4] The term "trinoda necessitas" was rarely used in Anglo-Saxon times: its only known use is in a grant of land near Pagham, Sussex from King Cædwalla of Wessex to Saint Wilfred.
[5][6] Instead of the term "trinoda necessitas", it was common for Anglo-Saxon land grants to spell out the three obligations individually.
For example, the land grant of Æthelberht of Kent to a thegn in 858 was free of obligation, except explicitly for military service, bridge repair, and fortification.