Complex sentence: After the death of Pope Leo IX, a Roman delegation headed by Hildebrand, later Pope Gregory VII, travelled to Mainz and asked the Emperor for the nomination of a successor and suggested Gebhard, who was duly nominated in September 1054.
Split into simpler sentences: After the death of Pope Leo IX, a Roman delegation headed by Hildebrand, later Pope Gregory VII, travelled to Mainz and asked the Emperor for the nomination of a successor. He suggested Gebhard, who was duly nominated in September 1054.