There are reputed to have been three Anglo-Saxon saints of this name:
1. A Mercian princess, daughter of Penda, who married Alcfrith, the son of Oswiu, king of Northumbria. She was foundress and abbess of the convent of Castor (Northants.). She died c.680 and was succeeded by her sister Cyneswith. The relics of these two sisters, together with those of their kinswoman Tibba, were translated to Peterborough and later to Thorney. Feast: 6 March, the day of their translation.
2. Cyniburg of Gloucester, to whom a chapel was dedicated there in 1147. Her Legend made her a princess who fled there to escape marriage and took employment as a baker's servant. His wife, motivated by jealousy, murdered her and threw her body into a well. She was taken up and buried near by; a church was built and miracles reported. For a long time, however, miracles ceased, supposedly because of the custodian's irreverence. Archbishop Courtenay ordered a fresh translation in 1390, accomplished by Henry of Wakefield, bishop of Worcester, on 10 April that year, after which miracles were renewed. Feast: 25 June.
3. Cyniburg, supposedly first abbess of Gloucester (according to the Gloucester Annals), claimed with other Mercian princesses as alumnae and benefactresses. If she ever existed (which seems doubtful), she should be identified with the abbess of Castor above. Or, more likely, her story could have been caused by confusing the other two Cyniburgs.
P. Grosjean in Anal. Boll., lxxiii (1955), pp. 350–1 and lxxix (1961), p. 168.