Hugh Candidus, a 12th-century chronicler of Peterborough Abbey, describes its foundation in the territory of the Gyrwas, under the name of Medeshamstede. Medeshamstede was clearly in the territory of the North Gyrwas. Hugh Candidus explains Gyrwas, which he uses in the present tense, as meaning people "who dwell in the fen, or hard by the fen, since a deep bog is called in the Saxon tongue Gyr". The territory of the South Gyrwas included Ely. Æthelthryth founded Ely monastery after the death of her husband Tondberht, who is described in Bede's Ecclesiastical History of the English People as a "prince of the South Gyrwas". Bede also described Thomas, Bishop of Dunwich, in East Anglia, as having been "from the province of the Gyrwas", and deacon to his predecessor, Felix of Burgundy.
- Potts, W.T.W., 'The Pre-Danish Estate of Peterborough Abbey', in Proceedings of the Cambridge Antiquarian Society 65, 1974: this paper contains some substantive errors, but is of interest.
- Mellows, William Thomas (ed. & trans.), The Peterborough Chronicle of Hugh Candidus, Peterborough Natural History, Scientific and Archæological Society, 1941, p2
- Bede, Ecclesiastical History, iv, 19
- Bede, op. cit., iii, 20.