Gregory’s pontificate witnessed the end of the iconoclasm controversy in the Byzantine Empire, while Gregory himself promoted the celebration of the feast of All Saints within the Frankish kingdom on both sides of the Rhine River. Gregory is also known for his appointment of Ansgar as archbishop of Hamburg-Bremen in 832, and as the apostolic legate to the northern and eastern parts of Europe. On 31 March 837 Gregory sent the Pallium to the archbishop of Salzburg; he also sent one to Venerius, the patriarch of Grado, in 828, in support of his claims to have jurisdiction over the bishops of Istria. When a synod awarded jurisdiction to Maxentius, the patriarch of Aquileia, Venerius appealed to Gregory, who supported him. Meanwhile, King Lothair backed Maxentius, who forced the bishops of Istria to obey him, while at the same time ignoring Gregory’s orders to cease. Gregory also supported the candidacy of John IV (bishop of Naples).