St. Peter was born of a noble family in Languedoc, about 1189. He founded the Order for the Redemption of Captives, and for twenty-five years toiled to release Christian captives from Turkish slavery. Worn out by his labors he died on Christmas Day, in 1256.
According to some, St. Agnes appeared to her parents eight days after her martyrdom. The ancient sacramentaries show clearly that this day celebrates the actual earthly birthday of St. Agnes; the nativity of John the Baptist and of the Blessed Virgin are thus celebrated because they were free from original sin; the earthly birth of St. Agnes is celebrated because her whole life abounded in divine grace.
(Source: Fr. Lasance, The New Roman Missal)