The historian al-Tabari transmits a tradition attributed to the Caliph Uthman who stated that the road to Constantinople was through Hispania, "Only through Spain can Constantinople be conquered. If you conquer (Spain) you will share the reward of those who conquer (Constantinople)." The conquest of Hispania followed the conquest of the Maghreb. Walter Kaegi says Tabari's tradition is dubious, arguing that conquest of the far western reaches of the Mediterranean Sea was motivated by military, political and religious opportunities. He considers that it was not a shift in direction due to the Muslims failing to conquer Constantinople in 678.