Cities and urban centres flourished along the Silk Roads passing through the Central Asian regions of Khorasan (in present-day North East Iran) and Transoxiana (a portion of Central Asia, that includes parts of present day Uzbekistan, Tajikistan, southern Kyrgyzstan and southwest Kazakhstan) between the 7th and 14th centuries CE. The transmission of cultures and ideas along with the movement of various trade wares along these routes had a significant effect on the architecture and layout of towns such as Samarkand, Bukhara and Merv. As these regions came under new influences, particularly from the Arabian Peninsula and China, various elements of architectural design were incorporated into pre-existing ones. These cultural interactions were apparent in the construction of monumental and decorative structures such as religious buildings, bathhouses, caravanserais, palaces, and as well as within carving and ornamental design.
Before the 9th century CE, the populations of Khorasan and Transoxiana predominantly lived in small settlements adjacent to fortified castles. In the 9th century CE, the region came under the influence of the Abbasid Caliphate one consequence of which was the rapid development of towns from the 9th to the 12th century CE in Khorasan, Transoxiana and Khwarazm (an oasis region between the Aral Sea and the Karakum desert). Generally, the pattern of urban development would involve the original pre-Islamic nucleus of the settlement being transformed into a fortified citadel, with a walled town built up around it. Outside this walled area, there would often be a trade and craft district comprised of shops and workshops.
From around the 10th century CE onwards, baked brick held together with a high strength gypsum mortar or ganch (the local name given to a building material used as plaster or mortar) was increasingly used in monumental architecture in these regions. Its use as a building material, for walls and vaulted domed structures provided architects with novel ways of putting recent advances in mathematics and applied geometry into practice. However, because it was a costly building material its use tended to be reserved for monumental architecture, and, in particular, buildings that needed to be waterproof such as bridges, piers and bathhouses.
Within architecture, geometric proportions were frequently employed with the ratio of the square and its diagonal being the most commonly used, although other ratios were also employed, such as the sides of a triangle or the Golden Ratio. A number of architectural designs were made possible thanks to significant mathematical progress made in academic centres such as Baghdad during this time, and in particular, in the development of applied geometry techniques. Here scholars synthesised mathematical knowledge from many regions of the world translating texts whilst working in an environment favourable to intellectual exchange. These applied geometry techniques were assimilated and widely employed by architects in regions along the Silk Roads of Central Asia.
In addition, caravanserai represented their own unique category of architectural design common to the Silk Roads. These roadside inns, where travellers and traders could rest on long journeys, were built in towns situated on the major land routes. Architecturally, they needed to provide safe shelter for caravans that had been travelling for many days, protecting from attack and theft, and provide enough space for animals such camels and horses to enter. Caravanserai often contained a central courtyard enclosed by a covered area for the summer quartering of pack animals and galleries for winter, with separate living quarters and utility rooms for travellers, large dining rooms, and areas for prayer.
Other developments in architecture and design that were introduced from the 12th to the 14th century included decorative features such as coloured glazed brick, and carved inlaid mosaic. Interiors were sometimes covered in polychrome painting, which made use of gold; one particular variety known as kundal, a wall painting technique producing a gilded relief painting typically using gold and blue with other colours including white, red and green for flowers and leaf tendrils. Later, in the first half of the fifteenth century, dark blue linear painting on a white background became popular in imitation of Chinese porcelain, a very popular ware that was exchanged across the Silk Roads.
In general, as urban centres built up along the Silk Roads of Central Asia the transmission and interaction of different cultures contributed to the shaping of various elements of architectural design. Some of these arose from advances in mathematics and particularly applied geometry developed in multicultural centres of learning, whilst others were specific to the necessities of long distance trade and travel, such as in the case of caravanserai.