Appendices - Strolling Through Istanbul: The Classic Guide to the City - page 481

The mosques of Istanbul fall into a small number of fairly
distinctive types of increasing complexity. The simplest of all, used
at all periods for the less costly buildings, is simply an oblong room
covered by a tiled pitched roof; often there was an interior wooden
dome, but most of these domes have perished in the frequent fires
and been replaced by flat ceilings. Second comes the square room
covered by a masonry dome resting directly on the walls. This was
generally small and simple but could sometimes take on monumental
proportions, as at Yavuz Selim Camii, and occasionally, as there, had
side rooms used as hostels for travelling dervishes. At a later period
in the eighteenth and nineteenth centuries a more elaborate form of
this type was adopted for the baroque mosques, usually with a small
projecting apse for the mihrab.
The next two types both date from an earlier period and are rare
in Istanbul. Third is the two-domed type, essentially a duplication of
the second, forming a long room divided by an open arch, each unit
being covered by a dome. It is derived from a style common in the
Bursa period of Ottoman architecture and hence often known as the
“Bursa type” (see the plan of Mahmut Paşa Camii). A modification
occurs when the second unit has only a semidome. Mosques of this
type always have side chambers. A fourth type, of which only two
examples occur in Istanbul, also derives from the earlier Selçuk and
Ottoman periods; a rectangular room covered by a multiplicity of
domes of equal size supported on pillars; this is often called the great
mosque or Ulu Cami type.
The mosques of the classical period - what most people think
of as the “typical” Ottoman mosques - are rather more elaborate.
They derive from a fusion of a native Turkish tradition with certain
elements of the plan of Haghia Sophia. The great imperial mosques
have a vast central dome supported on east and west by semidomes of
equal diameter. This strongly resembles the plan of Haghia Sophia,
but there are significant diferences, dictated partly by the native
tradition, partly by the requirements of Islamic ritual. In spite of its
domes Haghia Sophia is essentially a basilica, clearly divided into a
nave and side aisles by a curtain of columns both on ground floor and
gallery level. The mosques suppress this division by getting rid of as