It was like falling in love," says Norwegian artist Vebjorn Sand. "I just couldn't get it out of my mind." Six years ago, while visiting an exhibit of the works of Leonardo da Vinci, Sand became captivated by a model of a bridge that, in 1502, da Vinci had proposed building for Sultan Bajazet II, ruler of the Ottoman Empire. The Sultan wished to span the Golden Horn, an inlet between the Turkish cities of Pera and Constantinople (known today as Istanbul). At that time, it would have been one of the world's largest bridges. But to the astonishment of the Ottoman court, the proposed design took the form of a giant arch. After conferring with advisers, the sultan responded with what seemed like common sense -- an arch that big would collapse in the middle. He declined the proposal.