The third court houses the palace school for pages (enderun), the sultan's headquarters and his treasury. It is entered through the Gate of Felicity (Bab'üs Saadet) that is guarded by the White Eunuchs. Their barracks and the dormitories of the new students used to flank the gate prior to a fire in 1856; they have since been rebuilt as offices. The Sultan met the members of the Divan every day in the Chamber of Petitions (Arz Odasi), a large hall with a portico located immediately behind the gate. To the left are the Aviary Gate of the Harem and the exclusive kitchen of the Sultan next to the Mosque of the Aghas, which had separate sections for the pages and the harem women. Preceding the Royal Pavilion of Mehmed II (Has Oda) on the corner is the Dormitory of the 39 Senior Pages (Has Odalilar Kogusu) who performed personal services for the Sultan. The Royal Pavilion was used for the safeguarding of the Holy Mantle and other relics of the prophet brought from Cairo by Selim I (1512-1520) after sultans moved their apartments from here into the harem following the second half of the 16th century. Across the courtyard from the Pavilion of the Holy Mantle is the Inner Treasury (Iç Hazine) or the Kiosk of Mehmed II. Royal treasures were stored here and in an adjoining room that previously belonged to the Pages' Hamam that Ahmed I (1603-1617) had replaced by a dormitory for the expeditionary force, known as Campaign Hall (Seferli Kogusu). The three-story Library of Ahmed III occupies the center of the courtyard where the Pool Pavilion (Havuzlu Kösk) once stood. Dormitories of senior students in charge of the treasury and the cellars, The Hall of the Treasury (Hazine-i Hümayun Hademeleri Kogusu) and the Department of the Pantry and Stores (Kilerli Kogusu), separate the third court from the fourth. The halls of the third court are united by a portico that runs around the courtyard.
Sources:
Ayverdi, Ekrem Hakki. Osmanli mimarisinde Fatih devri, 855-886 (1451-1481), IV. Istanbul : Baha Matbaasi, 1973-74. pp: 682-755
Davis, Fanny. The Palace of Topkapi in Istanbul. New York: Scribner. 1970.
Goodwin, Godfrey. Topkapi Palace : an illustrated guide to its life & personalities. London: Saqi Books. 1999.
Necipoglu, Gülru. Architecture, ceremonial, and power : the Topkapi Palace in the fifteenth and sixteenth centuries. New York, N.Y. : Architectural History Foundation ; Cambridge, Mass. : MIT Press. 1991.