Complex sentence: After presiding over a synod at Pavia, he joined Henry III in Saxony, and accompanied him to Cologne and Aachen; to Reims he also summoned a meeting of the higher clergy, by which several important reforming decrees were passed.
Split into simpler sentences: After presiding over a synod at Pavia, he joined Henry III in Saxony and accompanied him to Cologne and Aachen. He also summoned a meeting of the higher clergy in Reims in which several important reforming decrees were passed.