Cáin Adomnáin (697) was a Brehon law which prohibited the killing of women and other non-combatants and forbade their use in warfare. It imposed penalties for rape, sexual harassment and other offences against women and against children and clerics. Adomnán was one of Colmcille’s successors as abbot of Iona from about 679 to 704 AD and both men were descended from the powerful Northern Uí Néill. Adomnán had sufficient prestige to assemble a conference of ninety-one powerful chieftains and clerics at Birr to promulgate the new law.
During almost two centuries, and more precisely the years 697-887, nine different ordinances were promulgated and kept in the record of the annals of Ireland. Each ordinance was issued either by a saint or monastic group. Three texts of these legislations have come to us, the earliest being Cáin Adomnáin – Lex Innocentium – proclaimed by Adomnán, abbot of Iona, at the synod of Birr in 697.
According to D.N. Dumville, it is suspected that the promulgation of this law in 697 was a centennial commemoration of Columba, who died in 597. As a successor of Columba of Iona, Adomnán had sufficient prestige to assemble a conference of 91 chieftains and clerics from Ireland, Dál Riata, and Pictland at Birr to promulgate the new law. As well as being the site of a significant monastery, associated with Saint Brendan of Birr, Birr was close to the boundary between the Uí Néill-dominated northern half of Ireland, and the southern half, where the kings of Munster ruled. It, therefore, represented a form of neutral ground where the rival kings and clerics of both sides of Ireland could meet.
Various factors, including Marian devotion in seventh- and eighth-century Ireland are supposed to have contributed to inspire Adomnán to introduce these laws.