Founded by Mustafa III, built 1759-1763, design by Mehmet Tahir Aga, "greatest and most original of the Turkish baroque architects" (I quote Strolling through Istanbul). It's built on a raised platform, and stands aloof from the busy Ordu Caddesi.

In the complex there is a mausoleum, this is a picture. Sultan Mustafa III (1717-1774) is described at the tomb as very well educated, interested in astrology and history, very religious and kind hearted. After an earthquake of two minutes that destroyed half of Istanbul he helped the people from his own wealth. He believed in the necessity for reform. He sent Ahmet Resmi Efendi to Frederick II of Prussia, who let Mustafa know (his) 4 secrets: Read history and examine the experiences; Have a powerful army and teach soldiers in time of peace. The sultan died of an heart attack in 1774 during the Ottoman-Russian War.

Sultan Selim III (1761-1808) was Mustafa III’s son. From the Wikipedia: Selim III (Ottoman Turkish: سليم ثالث Selīm-i sālis) (24 December 1761 – 28 or 29 July 1808) was the reform-minded Sultan of the Ottoman Empire from 1789 to 1807. The Janissaries eventually deposed and imprisoned him, and placed his cousin Mustafa on the throne as Mustafa IV. Selim was killed by a group of assassins subsequently after a Janissary revolt.