The complete ninefold plan -- as it became current in Mughal
architecture -- consists of a square (or rectangle), sometimes with corners fortified by
towers but more often chamfered so as to form an irregular octagon (termed muthamman
baghdadi by the Mughals). The layout is divided by four intersecting construction
lines into nine parts, comprising a domed chamber in the centre, rectangular open halls in
the middle of the sides -- in the form either of pishtaqs or of flat-roofed
verandahs supported by pillars (the Mughal iwan) -- and two-storey vaulted rooms or
blocks in the corners, reflected on the facade by superimposed vaulted niches (nashiman).
In the radially planned versions of this scheme the corner rooms are linked to the main
domed chamber by additional diagonal passages. The term hasht bihisht
("eight paradises") has been interpreted as a reference to the eight rooms
surrounding the central chamber. While in preserved Timurid architecture buildings with
such a strictly symmetrical ninefold plan represent the exception rather than the rule, it
is the characteristic contribution of Mughal architecture to have adopted and further
developed the model in a perfect symmetry faithfully reflected in the elevation. (Koch,
1991, p. 45)