Originally from Pamplona, he traveled through Northern Gaul to convert pagans and notables, which led to his arrest and decapitation by Roman authorities. He is represented in iconography holding a bishop's crozier and sometimes accompanied by the sword used in his torment.
Firmin was born in Pamplona, Spain, the son of a Roman senator. He was converted to Christianity by Saint Saturninus (or Saint Honoratus). He then traveled to Gaul to preach the Gospel. He became the first bishop of Amiens, where he established the Christian community. He was eventually arrested and martyred by decapitation during the persecutions of Diocletian or Maximian. His relics were discovered and translated in the 8th century, leading to a flourishing cult, particularly in Amiens and Pamplona, where he is the patron saint.