Complex sentence: He accepted their gift but then ordered it hang over the altar of Hagia Sophia as his own tribute to the church, which according to Theophanes was taken an insult by both Augustas and caused a rift in the marriage.
Split into simpler sentences: He accepted their gift but then ordered it hang over the altar of Hagia Sophia as his own tribute to the church. Which according to Theophanes was taken an insult by both Augustas and caused a rift in the marriage.