In order to get a better understanding of Sinan’s own architectural achievements, we must dwell a little on the architectural developments that preceded the them. Sinan’s greatest contribution lies in the innovations he brought to the architecture of the dome. In the Islamic world, domes were not used to cover the whole area of buildings, except in the case of some tombs, rather they of served to enhance buildings. Ottoman architecture, from its very first beginnings, had been an architecture of the dome. The Ottomans a virtually identified their mosques with domes, trying out every possible variant of the form. The role of Saint Sophia in this preference cannot be denied. The function of the dome was moreover not limited to covering a given area, it became a key element of the whole bearing system.
Single, multiple, pluri-based or multi-functional inverted T -shaped domed mosques and their neighboring domed tombs, departing from the old kumbet form, were already a typical Ottoman trait at the time when Bursa was the first capital to the empire (1326), together with domed medreses (theological schools), and domed hamams.
The Bursa style continued for some time after the city of Edirne became the second capital in 1368, but the Uc serefeli Mosque, built in Edirne by Murad II in 1447, played a pioneering role, proposing a kind of plan which was to be amply developed later. Innovative aspects like the hexagonal structure supporting its dome, its porticoed courtyard and its four minarets, do indeed give the mosque a character not typical orthe period.
After the conquest of Istanbul (1453), the Saint Sophia Basilica, which was much admired by the Ottomans, became a constant focus of interest for Turkish architects, who almost idolised it. The Fatih (Conqueror) Kullliye (a complex of religious and other accompanying buildings) was completed in 1471 under the reign of Mehmet II. With its sixteen medreses, its location and composition, the monumental complex put a Turkish stamp on the city. A semidome was added to the main dome of the original Fatih Mosque, probably under the influence of Saint Sophia, which brought the concept into the Ottoman architectural discourse. The old Fatih Mosque was still standing in Sinan’s time. It was to be destroyed by the 1776 earthquake. Also interesting is the Beyazid II Kulliye in Edirne (1488), with its pendentive supported 20 m wide single dome and especially the hexagonal shape and general composition of its hospital. The interior space of the mosque is dominated by the single dome. The side walls are laced with window openings and the system bearing the dome is almost unnoticeable. This anticipates the Edirnekapi Mihrimah Mosque, Sinan was to build some 80 years later. With its double semidome, the Beyazid II Mosque in Istanbul (1506) is an improved version of the old Fatih Mosque. The influence of Saint Sophi may also be felt here, but must not be considered simple copies.
Such are the stepping stones of the 250-year-old history of Ottoman architecture inherited by Sinan. The works mentioned above show that Ottoman architecture had already developed its identity by the time Sinan appeared.