During Late Antiquity, as a result of the viciousness of the wars between Celt and Saxon, Adomnán of Iona (an Irish abbot) put forth the Law of Innocents at the Synod of Birr in 697. This law aimed to protect non-combatants (the old, women, children and clergy) from attack. It was witnessed by 51 kings and local rulers along with 40 leading clergy.

Source: Celt and Saxon: The Struggle for Britain, AD 410-937 by Peter Berresford Ellis