The Cáin Adomnáin (Law of Adomnán), also known as the Lex Innocentium (Law of Innocents) was promulgated amongst a gathering of Irish, Dál Riatan and Pictish notables at the Synod of Birr in 697. It is named after its initiator Adomnán of Iona, ninth Abbot of Iona after St. Columba.
This set of laws were designed, among other things, to guarantee the safety and immunity of various types of non-combatants in warfare. It required, for example, that "...whoever slays a woman ... his right hand and his left foot shall be cut off before death, and then he shall die."
The laws also provided sanctions against the killing of children, clerics, clerical students and peasants on clerical lands; against rape, against impugning the chastity of a noblewoman, prohibited women from having to take part in warfare, and more besides. Many of these things were already crimes, either under the common Irish laws, or, in the case of special protections for clerics, from the Cáin Phátraic (Law of Saint Patrick), albeit with lesser penalties. Adomnán's initiative, however, appears to be one of the first systematic attempts to lessen the savagery of warfare among Christians - a remarkable achievement for a churchman on the remote outer edge of Europe.
As with later clerical efforts, such as the Peace and Truce of God movement in millennial France, the law may have been of limited effectiveness. Fergus Kelly notes that no cases relating to the Cáin Adomnáin have been preserved. Thus, we do not know whether the harsh penalties which it mandates, which may have contradicted the general character of Irish law, were rigidly enforced.
There are annalistic examples of the justice of the Cáin Adomnáin being applied, such as here by Cinel-Eóghain High King Niall Glúndubh, for whom the O'Neill Clan of Ulster are named.
- In 907 the sanctuary of Ard Macha was violated by Cearnachan mac Duilgen who took a captive from the church and drowned him in Lough Cier nearby.
- This perpetrator was taken by Nial Glundub mac Aedha, Righ an Tuaisceirt, having replaced his brother Domnall as king of the north, and he drowned Cearnachan in the same lake Lough Cier in revenge for the violation of Padraicc.
- "Law of the Innocents", Foghlam Alba
- Kelly, p. 79.
- Kelly, pp.234–235: "the law texts of the Senchas Már collection consistently favour reparation by payment rather than the death penalty for murder and other serious offences (by either sex)."
- Cf. Adomnán, Life, II, 24 and II, 25.
- Adomnán's Law of the Innocents - Cáin Adomnáin: A seventh-century law for the protection of non-combatants, translated by Gilbert Márkus. Kilmartin, Argyll: Kilmartin House Museum, 2008. ISBN 978-0-9533674-3-6
- Adomnán of Iona, Life of St Columba, edited & translated Richard Sharpe. London: Penguin, 1995. ISBN 0-14-044462-9
- Kelly, Fergus (1988). A Guide to Early Irish Law. Early Irish Law Series 3. Dublin: DIAS. ISBN 0901282952.