The invasion of Iran by the Arabs and the introduction of Islam to Iran substantially altered the appearance of classical Iranian architecture. First and foremost, in the new Islamic Iran, the construction of mosques replaced the construction of fi re temples. New mosques were built throughout the land, and in some cases former Sasanid temples were incorporated into mosques, as in the one at Yazd-e Khâst between Isfahan and Yazd. In the early period, mosques were fairly simple in design and functionality. As time went by, Iranian architectural know-how and taste influenced the construction and aesthetics of the mosques. Palace designs also began to acquire Islamic character. Although not many structures remain from the first two centuries of Islamic rule, there was rapid construction and expansion of Islamic buildings after the third century. The most distinctive architectural features of the Islamic period are the extremely elegant calligraphy, stucco, tile, mirror, and mosaic work used for decoration; the construction of tall towers; and the use of domes for mosques. Examples of the towers exist at Gonbad-e Qâbus (the tomb of Qâbus b. Vashmgir, built in a.d. 1006 with a height of 167 feet above and 35 feet below ground), at Shahr-e Rayy (the Gonbad-e Toghrel, built by the Saljuq ruler in a.d. 1139), and the Kâshâneh funerary tower at Bastâm (built ca. a.d . 1308). Mud brick towers from earlier periods have not survived, but those made from high quality brick and mortar still stand and are in good condition. The fact that many of these towers still remain is miraculous for a country prone to many devastating earthquakes. A spectacular feature of traditional Islamic architecture in Iran was the use of moqarnas . Moqarnas is an Arabic term to describe: a kind of stalactite decoration consisting of small nichelike components combined with each other in successive layers to enclose a space and generate surfaces rich in threedimensional geometric shapes. This technique is thought to have originated in eastern Iran and then to have spread throughout the whole of the Islamic world. Another impressive feature of ornamentation in Islamic architecture in Iran is its extensive use of calligraphy and fl oral designs in tiles and on doors. Calligraphic designs on tiles of deep azure blue, using phrases from the Koran or hadiths , have been used in almost all religious buildings. Walls, minarets, domes, and doors of religious shrines use these calligraphic designs not only for decoration and artistic quality, but also for producing a holy ambiance in the environment in which they are used. Most Islamic structures combine tile work, stucco and stone carving, illumination and moqarnas , joinery, gilding, embossing, latticework, inlay, raised work, and painting. The shrines of the Eighth Imam, Rezâ, in Mashhad; of Fâtemeh the Immaculate (Hazrat-e Ma‘sumeh) in Qom; of Shâh ‘Abd-ol-‘Azim in Rayy; and of Shâh Cherâgh in Shiraz are some of the most famous religious complexes in Iran, combining many forms of art in architecture and religious expression. The vast Imam Rezâ shrine (Âstân-e Qods) consists of 33 buildings with halls, porticos, ayvâns, and minarets all decorated with tile work, inlay, mirror work, stucco and stone carving, painting, illuminations, and moqarnas . Tiles are a major component of Islamic art and architecture, and the tile makers of Isfahan, Kâshân, and Rayy were known for their masterful work. As mentioned earlier, glazed brick had been an important element in the Iranian architecture and decorative arts since ancient times. Most of these glazed bricks were different from the kind of tiles used today. Brick and stucco were widely used for decorating buildings up to the tenth and eleventh centuries a.d. The acceptance of Islam increased the interest in the use of all kinds of designs, especially fl oral and calligraphic, in glazed bricks and tiles. Almost all mosques built in the Islamic period are decorated with these. The mosques at Nâ’in and Nayriz are the best examples of extensive use of geometric patterns in decorative bricks from the Buyid period. The mausoleum of Pir-e ‘Alamadâr and the tomb-tower of Mihmândust are other examples from the eleventh century a.d. Other cities have mosques with marvelous architectural work from this period, notably the congregational mosques ( masjed-e jâme‘ ’s) of Golpâyegân, Zavâreh, Qazvin, and Ardestân, all built during the twelfth century. The Il-Khanids in the thirteenth century a.d. used tiles not only for the exterior but also for the interior surfaces of the walls and domes. In fact, in this period, the use of tiles reached perfection in the form of mosaic-style design known as moraqqa‘ . Based on this technique, a panel is fi lled with previously cut and carved small pieces of tiles and then glazed. These glazed tile panels are more durable and weather resistant. The best early examples of these panels can be seen seen in the Timurid monuments of Herât, Samarqand, and Bukhârâ. Later monuments decorated with this technique include Gowharshâd Mosque in Mashhad, the Jâme‘ mosques of Yazd and Varâmin, and the Madraseh-ye Khân in Shiraz. Luster tile panel is another design consisting of square, rectangular, hexagonal, octagonal, and polygonal forms with human, fl oral, and geometrical motives. Most of these panels contained poetry, proverbs, and hadiths from religious or historical personalities. Sites at Takht-e Solaymân (especially from the palace of Abâqâ Khan in the Il-khanid period); Gorgân; Kâshân; and Khorâsân offer many examples of these panels. The calligraphic script known as ta‘liq became popular on tiles in the eleventh through fourteenth centuries a.d. Used in luster and under-glaze decoration, these tiles were inscribed with poems from Ferdowsi, Hâfez, Rumi, Sa‘di, and other famous Persian poets. During the Safavid period, naskh and soluth scripts also became popular. During the Saljuq period, the dome chamber type of mosque became the dominant model. The first double-shell domes were constructed. A defi ning feature of Saljuq architecture was stone and stucco carvings. The mehrâbs of the Jâme‘ mosques of Qazvin and Ardestân represent two examples of stuccocarving in this period. The Mongol invasion slowed artistic and architectural production until the thirteenth century a.d. when the Il-Khanids accepted Islam and became interested in promoting the arts. A new form of stucco art, found in the Haydariyeh Madraseh at Qazvin, was introduced during the Mongol period. A different kind of vaulting technique that required precise calculation of size and dimension in the construction of domes was also introduced under the Timurids. Designs of these domes are indicative of some Chinese influences. The Vaqt o Sâ‘at complex in Yazd is another example of the sophistication of structures in this period. Commissioned by Sayyed Rokn-od-Din and completed around 1326, it originally included a mosque, library, seminary, and observatory. Part of the complex, usually called the Masjed-e Vaqt o Sâ’at, a domed building decorated with naskh and kufi calligraphic inscriptions, still stands today. The Safavids were great supporters of the arts, and one of the most productive artistic periods in Iranian history developed under their patronage. The city of Isfahan in particular was turned into a virtual museum of exquisite architectural monuments, adding to the city’s already rich cultural heritage. The infrastructure of the city was greatly improved, and attention was given to not only the construction of palaces and mosques, but also to utilitarian structures such as caravansaries, bridges, bazaars, bathhouses, water reservoirs, dams, and pigeon cots. Magnifi cent gardens and palaces were built. The garden plays a symbolic role in Persian imagination and is the landscape on which the Iranian sense of beauty grows, but the palace is the ultimate desire of Iranian ruling elites. A fi ne example of a Safavid palace and garden in Isfahan is the Chehel Sotun, a palace built in the middle of the Jahân-namâ Garden. Its ceilings are supported on tall wooden columns on stone plinths decorated with fi ne wooden frames of different geometrical designs; the walls have latticed windows, mirror-work, and paintings of Safavid rulers, battles, and ceremonies. The large pool in front of the palace creates a natural mirror for the refl ection of the palace. The heart of Safavid Isfahan was the Maydân-e Naqsh-e Jahân, a huge square at the center of the city fl anked by the Masjed-e-Shah (now called Masjed-e Emâm), Masjed-e Shaykh Lotfollâh, and the ‘Âli-qâpu Palace (a government structure built at the time with six stories). The tiles in the mosques on the Naqsh-e Jahân are decorated with beautiful inscriptions of verses from the Koran in deep azure blue. The northern part of the Naqsh-e Jahân square leads to the great bazaar of Isfahan—one of the most attractive and frequented bazaars in Iran. In general, the Safavids concentrated on the exterior grandeur of their buildings, which they emphasized by building recessed structures like niches and entrances that gave a sense of depth. Tile work was also implemented on a larger scale and covered vast surfaces. These buildings have been subject of numerous books by art historians and architectural experts. The Safavids also built a number of magnifi cent bridges. In Isfahan, the Khâju bridge served as both a bridge and a dam, It is one of the most elaborate combined bridge-dams in the world. The second fl oor of the bridge contains beautiful pavilions decorated with stucco carvings and inscriptions. Finally, it should be mentioned that the policies of Shah ‘Abbâs encouraged the transfer of a large number of religious minorities to Isfahan. This resulted in construction of some beautiful Armenian churches in Jolfa on the southern side of the Zâyandeh Rud river as well as in Shiraz. During the Afsharid and Zand periods, there were few new developments, except the application of different colors in glazed tiles. The Kâkh-e Khorshid palace and the observation tower in the city of Kalât were built during the reign of Nâder Shah. Karim Khân Zand, who made Shiraz his seat of government, built a citadel, a bazaar, and several bathhouses, all named after him. A distinctive pink tile, known as Zand tile, was developed during this period. Overall, Iranian architecture experienced a decline in the Qâjâr period as many old monuments remained in disrepair. Though many new structures were built, none could reproduce the grandeur and the glory of the previous era, especially the Safavid period. Several city gates, with monumental decorative ceramic works, and many mosques, with numerous ayvâns, networks of cupolas, and more windows for lighting were built. Buildings erected in this period had deeper courtyards and ceilings and walls decorated with mirrors. Military architecture received new attention as Iran began to learn about new European military developments. Members of the elite enthusiastically built palaces, mansions, pavilions, and hunting and summer resorts. The Masjed-e Shâh and Masjed-e Sepahsâlâr are two of the important mosques built in Tehran during this period. The arrival of Europeans resulted in the construction of a number of new churches, adding to the number built in Iran in earlier periods. During the reign of Fath-‘Ali Shah, the crown prince and governor of Azerbaijan, ‘Abbâs Mirzâ, ordered new structures to be added to the Saint Tâtâvus monastery, known as the Qara Kelissâ . The Saint Tâtâvus Church, located in one of the oldest districts of Tehran, was also built during Fath-‘Ali Shah’s reign. A church built in this period in Bushehr represents one of the best examples of the application of Iranian architecture to a Christian building. The artwork and windows were all based on old Iranian designs.