The Sultan Ahmed Mosque — known worldwide as the Blue Mosque — is perhaps the most beautiful and imposing Ottoman house of worship ever built. It was constructed between 1609 and 1616 on the orders of Sultan Ahmed I — a young ruler who came to the throne at just 13 years of age and sought to give his reign lasting significance through a monumental building. It was designed by Sedefkâr Mehmed Ağa, a student of the great architect Sinan, who took his teacher's architectural language and brought it to a new point of perfection. What immediately sets the Blue Mosque apart from every other Islamic house of prayer in the world is its skyline: six minarets. This was controversial. Until then, only the Kaaba in Mecca had six minarets, and critics saw the choice as an act of presumption. Sultan Ahmed responded by having a seventh minaret added to the Kaaba to resolve the dispute. Today these six slender towers, together with the five cascading domes, define the skyline of Istanbul more powerfully than any other building. The interior of the mosque is a feast for every sense. Over 20,000 handcrafted Iznik tiles cover the walls from floor to shoulder height — in more than fifty different motifs of tulips, carnations and climbing vines, all in cobalt blue, turquoise, emerald green and white. It is precisely this incomparable blue that gave the mosque its famous nickname. The tiles come from Iznik (ancient Nicaea), the center of Ottoman ceramic art, and their quality has never been equaled by industrial reproduction. Light plays a role in the Blue Mosque equal to that of the craftwork. Two hundred and sixty windows — originally glazed with Venetian stained glass — bathe the interior in a soft, shimmering radiance. This light falls across the crimson prayer carpet, the many hanging brass lamps, and the white marble pavilion of the mihrab — the prayer niche pointing toward Mecca. To enter the mosque during the call to prayer, or to witness the communal act of worship, is to encounter Istanbul at its deepest and most mysterious. The mosque is an active place of worship, not a museum — a distinction that shapes every visit. Tourists enter through a separate gate and should wear shoulder-covering clothing; women are asked to cover their hair, and free-loan scarves are available at the entrance. In front of the mosque stretches the broad Sultanahmet Square, once the Hippodrome of Byzantium. Here still stand the Egyptian Obelisk of Pharaoh Thutmose III, the Serpent Column from Delphi, and the Walled Obelisk of Constantine VII — silent witnesses to three thousand years of world history. The combination of the Blue Mosque, the Hagia Sophia across the way, the sunken Hippodrome, and the Topkapi Palace makes the Sultanahmet district the most densely layered historical space in Europe. Visitors are advised to arrive early in the morning before the first wave of tourists, or shortly after the midday prayer, when the mosque reopens. The view from the forecourt at dusk, when the minarets are illuminated, is one of the most romantic sights in all of Istanbul. The Blue Mosque is not merely a house of prayer — it is a soul built from stone, faience and light.