TRINODA NECESSITAS, the name used by modern historians to describe the threefold obligation of serving in the host (fyrd), repairing and constructing bridges (bryc-geweorc), and the construction and maintenance of fortresses (burhbot), to which all freeholders were subject in Anglo-Saxon times. The obligations are usually mentioned in charters as the sole exceptions to grants of immunities; sometimes, however, a fourth obligation (singulare praetium contra alium) is reserved, as in the charter granted by Wiglaf of Mercia on the 28th of December 831 (Cod. dip. i. 294). Ceolwulf's charter of 822 to Archbishop Wilfred is remarkable, as the military service is there restricted to expeditiones contra paganos ostes (ibid. i. 272). The threefold obligation is first mentioned in a Latin charter (expeditione pontis arcisue constructione) of doubtful authenticity, which professes to have been granted by Eadbald of Kent in A.D. 616 (Cod. dip. v. 2), but it is not until the 8th century that it appears in documents which are generally admitted to be genuine. Although there were corresponding obligations in the Prankish Empire which were called by Charles the Bald (antiquam et aliarum gentium consuetudinem) , Stubbs held that the arguments which refer them to a Roman origin want both congruity and continuity.
The phrase " trinoda necessitas " is not to be found in the AngloSaxon laws and charters; and Selden was probably the first historian of eminence who used it. " These three exceptions," he says, " are noted by the term of a three-knotted necessity in an old charter wherein King Cedwalla granted to Wilfrid, the first bishop of Shelsey in Sussex, the village of Paganham." This charter is an nth-century copy of a lost original, but the words to which Selden referred are plainly written as trimoda necessitas not trinodanecessitas. Du Cange gives two examples of the word trimoda in medieval Latin, in which language it meant "triple"; but he cites no medieval example of trinoda; and in classical Latin the form is unknown, while trinodis (ter-nodus, " triple-knotted ") occurs only rarely (Ovid. Her. iv. 115; Fast. i. 575).
See Du Cange, Glossarium ; W. Stubbs, The Constitutional History of England, i. 86, 87; J. M. Kemble, Codex anglo-saxonicus, passim; Selden, English Janus (London, 1682), p. 43; Walter de Gray Birch, Cartttlarium saxonicum, passim; Facsimiles of Ancient Charters in the British Museum, pt. iv. Cotton MS. Augustus, ii. 86. (G. J. T.)
Note - this article incorporates content from Encyclopaedia Britannica, Eleventh Edition, (1910-1911)