As a major building material, brick also determined the form taken by the buildings' various types of vaulting and domed roofs. The round base of the dome, where it met the top of a square room, was determined by its ground plan; the transition between circle and square was achieved by means of squinches, i.e. arches spanning the corners of the square, forming the octagonal lower part of the dome. Console spandrels were also known, consisting of rows of superimposed brick brackets.

These formed the basis of the stalactite structures (muqarnas) which had already appeared in the 11th century and which later became very widespread. The arches, and therefore the cross-section of vault and dome too, were generally pointed. Here, a geometrical procedure allowed an infinite number of variations on the pointed arch to be developed.
 

Squinch in the Kyz-Bibi Mausoleum in Merv, 11-12th centuries The squinches in this clay brick building take the form of the stepped, arched design previously widespread throughout Central Asia. This building represents one of the last examples of pre-Islamic architecture.

In the 11th century the first buildings - mausoleums - were built with double-shell domes, a technique that rapidly became widespread in monumental architecture. In this way the outer shell of the dome, resting on a drum, could be transformed into an impressive structure whose shape was independent of the building's interior. In the 12th century the outer shell of the dome was sometimes given a steep pyramid or conical shape, which afforded the dome better protection against rain and snow.

The limitless variety of ground plan and interior designs in the architecture of Central Asia between the 11th and
beginning of the 13th centuries can be reduced to two basic schemata: the courtyard-axis schema and the central dome structure. The first of these consists of a rectangular courtyard with two right-angular axes, the longitudinal axis being the main one, enclosed by buildings forming a rectangular outline. This schema was used for large buildings of both sacred and secular function, such as mosques, palaces, madrasas, and caravanserais. The simplest design was that of the courtyard mosque, where the space between the courtyard and windowless exterior wall was occupied by a continuous gallery. This consisted of several rows of brick piers forming continuous domed cells generally connected to each other by archways. Stone or brick columns were not used because of the frequent earthquakes in Central Asia.

Most of the surviving 11th and 12th century caravanserais, which served as inns for traveling merchants and their
caravans, and often developed into trading centers themselves, stand out because of their combination of magnificence and functionality. They frequently had an impressive palace-like character. Here too the longitudinal axis dominates, beginning at a monumental entrance portal and continuing through one or two courtyards surrounded by various types of rooms (accommodation for the traders, storage for goods, stables) and ending in a suite of splendid halls. The numerous functions of the caravanserais explain the complexity of their design and the differences between the concrete forms they took.
 

Stepped console spandrel in the Daya Khatun Caravanserai, 11-12th centuries Console supports of this type were the precursors of the weight-bearing as well as decorative muqarnas structures that were to become widely used in Islamic architecture in the following century.

Not much has been known about the architecture of the 11th and 12th Century Central Asian madrasa for very long, the one definite example of it that has so far been discovered being the Khoja Mashhad madrasa in southern Tajikistan. This building shows that madrasas from this period already displayed the important features of madrasa design that were later to become the norm.

Central Asian palace complexes served on the one hand as the private residences of the rulers, but always, on the other, incorporated an official series of rooms that accommodated the authorities, and where officials carried out affairs of state. In the 11th and 12th centuries, these buildings were also as a rule constructed along the lines of the old courtyard-axis schema. Their starting point was the courtyard, whose primary axis led from a ceremonial portal through to a vaulted hall or iwan, completely open to the Courtyard. This is where the ruler would hold his audiences, while the public was confined to the courtyard. While the architecture of the palaces was strongly influenced by the local building traditions, the courtyard principle, despite numerous variations, was common to all of them. Sometimes, however, the semantic and compositional center of the palace was not a vaulted throne iwan, but a domed hall. Whether the individual palaces and official residences of the 11th and 12th centuries known about as a result of excavations followed the axis principle or not, their layout, in keeping with their wider range of functions, was essentially more complicated than that of the courtyard mosques, madrasas, and even caravanserais.

Detail of portal of the Khoja Nakhshran Mausoleum near Regar, Tajikistan, 11-12th centuries This is a particularly well-executed example of typical decorative brickwork arranged in double bonds with decorative elements of carved terracotta. The corner column is an example of the use of decorative elements to a structural end. The Kufic inscription and decorative embellishments alongside it are cut from specially baked pieces of clay.

This multifunctionality was typical of the complexes of the 11th and 12th centuries built according to the courtyard-axis schema; thus the courtyard mosques, for example, were also public, municipal centers and could additionally serve as fortresses at times of danger. The similar architectonic structure in each case permitted variations of function: caravanserais, madrasas, and even Friday (congregational) mosques could, under certain circumstances, undergo changes of basic function, or take on additional functions, without a fundamental alteration to their ground plan and room structure. Characteristic of the courtyard-axis structure, however, is its clear, rectangular basic shape and general symmetry with longitudinal and often transverse axis too.

The second design schema employed during this period, that of the central domed structure, found its realization in a design featuring identical, or near identical, symmetrical axes and a dominant dome-covered central building. In contrast to the dynamic courtyard-axis scheme, this design was by its very nature static. Both schemata had their origins in antiquity and had been used in various different ways in pre-Islamic buildings.

The simplicity of the domed hall design allowed it to be used for a variety of purposes and also to be combined with other rooms. The domed hall could form a single building and as such serve as a domed mosque or mausoleum; it could form the nucleus of a centralized building with a number OF rooms; it could be positioned at one end of the longitudinal axis of a courtyard complex; or form a constituent part of other combinations. The floor plan of a domed hall is seldom that of a simple square. In most cases its space was increased by means of vaulted niches on the cross-axis, which rendered it cruciform. Its main axis would usually be accentuated by a portal or pishtaq (Persian: "fore-arch"). This consisted of a high, vaulted niche within a rectangular frame with an entranceway at the back of it.

Detail of the interior decoration of the Hakim Termezi Mausoleum in Termez, 11-12th centuries The Termez mausoleum is a rare example of a small, domed building decorated from top to bottom with carved stucco. The walls are covered with a "lily pattern," framed within a continuous interlaced design. This is topped by a wide Kufic script frieze with an ornamental infill between the letters. The dome decoration is based on round gerich medallions with a geometric star pattern.
 

Already in pre-Islam times, Central Asian buildings had followed a schema of proportions that firstly served a practical purpose and secondly guaranteed a harmony of architecture. Later on, in the 11th and 12th centuries, mathematical discoveries were exploited in order to extend this system and thus opened up its possibilities. Widespread use was made of grid screens containing square cells, the length of whose sides corresponded to the length of the arm from shoulder to fingertips. These grids were used to fix the measurements for the domed rooms and their axial niches, the thickness of the walls, the width of the entrance and so on.

The essential characteristics of Central Asian architecture from the 11th to the beginning of the 13th century, such as its unity of construction and decoration, its mathematical harmony of form, and its minimal number of basic design schemata which could be realized in endless variations, allow it to be seen as classical and thus comparable with that of classical Greek antiquity.