The Synod of Mantaille
was held in Mantaille
, in the southwestern rench region of Provence
, on 15 October 879
by the bishops and nobles of the region around the rivers Rhône
. They elected Boso of Provence
, Count of Vienne
, as successor to king Louis II of France
, dead since April.
The synod marks the first occurrence of a "free election" among the Franks, without regard to royal descent, inspired by the principles of ecclesiastical elections.