The cascading domes and six slender minarets of the Sultanahmet Mosque (better known as the “Blue Mosque”) dominate the skyline of Istanbul. In the 17th century, Sultan Ahmet I wished to build an Islamic place of worship that would be even better than the Hagia Sophia, and the mosque named for him is the result. The two great architectural achievements now stand next to each other in Istanbul’s main square, and it is up to visitors to decide which is more impressive.