A trip to Istanbul has made me think about the characteristics of the mosque as an architectural form. It's interesting to follow the way Hagia Sophia influenced the mosques in Istanbul - and the many ways in which its invitations were refused by Islamic architects.
First, obviously, the idea of a huge domed space was influential. But this was already present in Seljuk architecture a long time before the Turks became acquainted with the heritage of Constantinople. None the less, there's some evidence that architects such as Mimar Sinan, looking at Hagia Sophia, learned new engineering techniques - specifically, buttressing using exedrae (semidomes) to counter the thrust, the use of turrets to buttress the dome, and the creation of series of cupolas falling away from the main dome which creates the distinctive Ottoman profile - very different from the simple skyline of earlier mosques.
The idea of the dome as representing heaven is common to both the Greek and the Islamic architecture, too.
But now what differs very substantially is the feeling for space. Hagia Sofia is divided up into different zones, only half visible from each other. There's a narthex, an exonarthex, a gallery, whole areas in the corners which seem hidden in some exclusive penumbra, which have no visibility of the central dome. There's even a huge carved marble screen in the south gallery to divide off the Synod's meeting area - and the fact that it is carved in the shape of two fake doors makes it nature as an instrument of closure unmistakable. This is a building made to exclude, to divide, to separate.
By comparison the mosque is a zone of inclusion, with the single exception of the women's gallery. Even when the sultans began to divide themselves off from the remainder of the worshippers, the main architectural feature was the external ramp leading to the sultan's gallery - inside the mosque the sultan's loge is often discreet and hardly visible, except in the magnificence of its decoration. Most mosques appear to strive for unbroken space - the arcades that screen off the aisles of Hagia Sophia almost never appear.
There's another interesting thing about the mosque. It pretty much has to be square. (There is one oval one, apparently, out near Yedikule, and it's a very late baroque mosque. Also, a private mosque - not founded by a sultan and so perhaps less exposed to objections from the Ulema.) That of course gives the architects all kinds of problems in sticking a dome on top. But it also means that creating a baroque style is difficult, because you have to have a square, which is an anti-baroque, classical form.
Architects got round this in different ways. At Nurosmaniye mosque near the Grand Bazaar, the architect created a horseshoe shaped courtyard. In other mosques, the galleries are used to create a feeling of dynamism within the square. But the real successes of baroque form aren't the mosques - they're the lovely fountains and 'sebils' (waterhouses from which refreshments are served) often placed on the corner of the mosque precinct. Here, the round form let architects play with concave and convex forms - the grilles of the windows, the overhanging eaves of the roof. One of the nicest shadirvans (ablution fountains) is that in the courtyard of Hagia Sophia - and I bet of the thousands of people who visit every day, barely any of them give it a glance. It's lovely, and the delicate grilles are as good as anything in the church.
And that brings me to the last thing I learned about the Ottoman mosque. You can't see a mosque as just a mosque, because in almost all cases it's the centre of a complex ecosystem a little like the English cathedral close. Suleimaniye for instance was built within a fine precinct wall, with areas both sides where caravans could spend the night with their camels and tents; there's a graveyard with the mausoleums of Suleiman the Magnificent and Haseki Hurrem, better known as Roxelana, his wife; outside the precinct wall are a row of shops (arasta) designed to pay rent to the mosque, so the development was self funding; there are four separate medrese (schools), a sibyan mekteb or primary school, a hamam (bath), a doctorate school of law, a cistern, a hospital, a kitchen (now a restaurant) and a hospice where travellers were entitled to spend three nights free. Even the houses of the professors at two of the medrese have been included as part of the package.
This is the biggest and best planned unit in Istanbul, but even small mosques like Rustempasha Cami are at the heart of a little community. Here, the mosque is built up above a vaulted basement, with shops in it - you take a little twisting stair up between two shops to arrive suddenly in the light, open portico in front of the mosque. To both sides of the mosque, trading hans were built, and the little shadirvan has been tucked away on one side, below. And of course there's the minaret.
Minarets, by the way, were one of the ways of indicating the status of a mosque. A regular mosque had one; foundations by members of the ruling family were entitled to two; some sultans' mosques have four (like Suleimaniye); and Sultanahmet, daringly, has six.