The Sultan Ahmet Mosque is better known as the Blue Mosque, because of its incredible interior.
The Blue Mosque was commissioned in the 17th century by 19 year old Sultan Ahmet I. Started in 1609, it was finished in 1616. He wanted to build a more impressive mosque than the AyaSofya. You can see both from either side of the same street in Sultanahmet. The Sultan passed away just one year after it was completed.Six minarets were built, which apparently upset some folks who felt only the mosque in Mecca should have six. Folklore says that he actually asked for four made out of gold (altin) and the word was misunderstood to be six (alti.). To make amends he sent his architect to Mecca to add a seventh to theirs.
Minarets are mainly built to give an advantage point for the call to prayer (adhan) which is issued five times each day: dawn, noon, mid-afternoon, sunset, and night. As a visitor the sound of adhan accentuates your visit to a foreign land, adding another facet to the sense of mystery and romance.
The tremendous size and architectural beauty of these centers of worship throughout Europe were built before we had cranes for multiple story building and other labor saving devices. Tons of money were spent by powerful religious organizations and many many people worked and died building them. If you have an interest in this, but like me prefer novels that bring it to life over a bunch of facts you might want to check out Ken Follett's The Pillars of the Earth. Yes, the same author who wrote Eye of the Needle and other spy thrillers has taken his attention to detail and his interest in the great cathedrals and created a three part series starting with this book.