marble shadirvan or ablutions fountain in the center of the courtyard, made of carved and pierced stone, is one of the finest examples of its kind from this period, but it lacks the usual roof and canopy. Doğan Kuban believes that this indicates it was never completed, while Gülru Necipoğlu states that this merely further emphasizes the view of the mosque's main dome above. The entrance portal to the mosque's prayer hall has more typical muqarnas canopy, while the dome covering the space in front of it is heavily fluted and decorated. The wooden doors of the entrance are said to have been taken from the Ulu Cami (Great Mosque) of Birgi. Prayer hall and main dome The prayer hall's interior is notable for being completely dominated by a single massive dome, whose view is unimpeded by the structural elements seen in other large domed mosques before this. This design is the culmination of Sinan's spatial experiments, making use of the "octagonal baldaquin" design he had experimented with earlier. In this design the main dome is supported by a system of eight pillars incised in a rectangular shell of walls. This was the most effective available method of integrating the round dome with the rectangular hall below while minimizing the space occupied by the supporting elements of the dome. The ingenuity of the mosque's design lies in the organization of its interior space. All of the architectural elements are subordinated to the huge central dome. The eight massive pillars are partly freestanding but closely integrated with the outer walls. Additional outer buttresses are concealed in the outer shell of the mosque, allowing the walls in between them to be pierced with a large number of windows. Four semi-domes at the corners, between the main pillars, are intermediary sections between the walls and the main dome. Compared to the semi-domes in some other Ottoman mosques, they are much smaller in relation to the main dome. Sinan also made good use of the spaces between the supporting pillars and buttresses by filling them with an elevated gallery inside the prayer hall, matched on the outside by arched porticos. The elevated galleries inside help to eliminate what little ground-level space exists beyond the central domed baldaquin structure, ensuring that the dome therefore dominated the view from anywhere a visitor could stand. Another of Sinan's primary objectives was to surpass the size of the