Sinan was around 40 years old when he built this mosque complex for Mihrimah Sultan, the daughter of Süleyman the Magnificent and wife of Rüstem Pasa. It was his second imperial commission after becoming Chief Architect, a post he earned thanks to the great civil engineering works he created while serving in the Ottoman army. In the design of the mosque, Sinan reinterpreted the theme of the square-based plan surmounted by a single dome by transferring the weight-bearing responsibilities from the four walls to an innovative system comprised of four arches and four pendatives. The central dome of the mosque is supported not by two or four semidomes, but three. This transfer of weight freed the walls to sustain a lacework of rosette and arched windows, allowing a flood of light into the interior space. The baroque-style minaret dates to the 19th century. At the base of the mosque is another baroque work, the monumental Ahmet II Fountain, built in 1728 by Sultan Ahmet III for his mother, who is buried in Üsküdar. A calligraphic poem by the sultan is inscribed on the side facing the sea, with his signature below.