Regarding the pre-Islamic era, the only important remains of Persian architecture are those of the extraordinary Ziggurat elamita of Choga Zanbil. In ancient times, building materials consisted essentially of sun-dried mud bricks; the fired bricks began to be used for external surfaces only from the twelfth century BC The ancient inhabitants of the Iranian plateau attributed great symbolic-religious value to the mountains, and in imitation of the mountains were built structures, just like the great pyramidal temples called ziggurat.
With the passing of the centuries, the two most important influences on architectural styles were those exercised first by the religion of Zarathustra and then by Islam. Most of the larger buildings were built for religious purposes, but the influences of religion were evident even in buildings destined for other uses - even Christian churches in Persia would often include Islamic elements.
On the other hand, the architecture of the buildings changed considerably depending on the period. At the time of Cyrus, for example, they were oblong in shape, exquisite proportions, and generally finished in contrasting colors. The palaces of Dario and Serse were larger and of better quality, but rather heavy and lacking in color, characterized by elaborate sculptures in the entrances, on the steps and on the columns. The most usual design consisted of a large hall with columns, surrounded by smaller rooms; another distinctive feature was the recourse to the niches next to the windows, which can still be found today in the Persian houses. The materials used included rough bricks for the walls, local extraction stones for the windows, the entrances and part of the walls and columns, and heavy wooden beams for the roofs.
The conquest of Alexander the Great virtually put an end to the Achaemenid style in Persia, and initiated the introduction into the country of Hellenism under the Seleucids. Not many important examples remain, apart from the Temple of Anahita in Kangavar, with Greek capitals, built in honor of a Greek divinity (Artemis).
In the epoch of the Parties there was a sort of contamination, or fusion, between the Hellenism and the indigenous styles, accompanied by some Roman and Byzantine influence, but at the same time several elements typically Persian appeared, such as the eivan, the great hall- portal with open barrel vault.
The art of Islamic Iran is largely based on that of the Sassanids, but it is limited to some forms. In other words, the Arab invasion of the seventh century did not supplant the Sassanid style, so well developed, but introduced the Islamic factor that exerted a pervasive influence on most of the Persian artistic forms, both shaping nature and the basic architectural design. of religious buildings, both defining the type of decoration.
Most Iranian mosques conform, in whole or in part, to a design that in Iran must be considered the norm. It consists of a large central open space, where you can sometimes plant trees and flowers, with a large eivan that opens on the side facing Mecca and leads into a sanctuary covered by a dome. On the other three sides of the central space there are arches and altars, and in the center of each one we find a smaller eivan. On the left and on the right of the sanctuary there can be rooms with arches, and also loggias (where women are often gathered) from which you can see the mehrab, the niche that indicates the direction of the Qaaba, in front of which the faithful pray. In the larger mosques, the southern eivan, which often forms the main entrance, is flanked by minarets.
The first minarets were square, at least for the lower floors, but few of them remain in today's Iran. The cylindrical minarets were born in the north-east of Iran: they were made of bricks and tapered towards the summit. Until the 13th century they were almost always single and placed in the northern corner of the mosque. In the fifteenth century began to be covered with mosaics or colored tiles, according to the taste of the time. But in the country the minarets are few in number compared, for example, to Turkey; only in Isfahan occupy a prominent place in the landscape.
The shrines, or sepulchres of saints, are very common in Iran: they are found in almost all the cities, and the village shrines or built along the streets are a typical element of the Persian landscape. Generally they are modest, circular or square or octagonal buildings, surmounted by a dome or a cone. Many are suggestive but devoid of great architectural value, and take on distinctive regional features; the most famous shrines, "in progress" structures to which every generation of devotees adds some elements, are however among the most splendid, and sometimes the most opulent, buildings of the country.
The secular tombs are divided into two large architectural categories: domed mausoleums and tower tombs. The former have some affinity with the larger shrines: they are often octagonal and flow into a circular dome, they are built to be visited and admired on the outside as on the inside, in order to inspire reverence towards non-religious figures but worthy of being remembered . Tower tombs, typical of northern Iran, were conceived in a very different spirit: as solitary and remote resting places, not destined to be frequented or admired by visitors.
As for the buildings, there remain many testimonies of the Achaemenid and Sassanid era, buildings that are impressive both in terms of size and quality of details; and some of them have been preserved almost miraculously, as in Persepolis. All traces of the royal residences of the Seljuks and Mongols have been lost. The royal palaces of the Safavids remain, but only in the area of Isfahan.
Finally, the caravanserais deserve a separate mention. Along the Silk Road, over the centuries, many public buildings were constructed, that is, intended for collective use, such as caravanserais or Ab-Anbar, underground cisterns for water collection and storage. Caravanserais were used both as hotels for parking, and as warehouses for goods, and the variety of their architectural and stylistic forms is due to numerous factors, economic, military and in many cases religious.
Along the route from Khorassan to Kermanshah, which crosses different areas such as the Semnan regions, the Central Region, the Tehran region and the Hamedan region, you can still see several caravanserais, mostly built during the Safavid period - some however they date back to the pre-Islamic period, others, more recent, belong to the Qajar era. However, all suffer from the ravages of time, and in a certain number of cases (such as that of Sar-e Pol-e Zahab, from the Safavid period, whose brick structure with four arcades is in deplorable conditions, despite speak of its possible recovery) only ruins can be observed, as a consequence of the damage caused by floods and earthquakes.
The most important caravanserai are found in today's Khorassan region. Mahidasht, built in the Safavid era, then restored and put into operation in 1893 by Nasser ad-Din Shah Qajar, is located north-east of the town of the same name, and consists of four porticos. The central courtyard is a square space of seventy meters on the side; the entrance portal opens on the south side, and crossing it you enter a vestibule with a domed ceiling which in turn connects with the southern portico. The portal plinth is in stone: it is located between the two eastern and western arches and extends to where the vestibule begins. On each of the two sides of the entrance you can see five double arches and two decorative arches in function of alcoves. Once in the caravanserai, two small arches are observed, each one one meter wide and two high, both leading to the domed chambers.
Seventy kilometers west of Kermanshah, on the road that leads from this city to Karbala, a place particularly revered by the Shi'ites because the site of the tomb of the saint Imam Hossein who was martyred in that place, meets the caravanserai of Islamabad-e Qarb ("Islamabad West"). At the time of its peak, this was probably one of the most beautiful and popular caravanserai in the Kermanshah area. It is composed of four porticos, and the central courtyard has a rectangular shape. The entrance, on the south side, is richly decorated, much more so than those of the other caravanserai of the region. Like the previous one, this too dates back to the Safavid era and was restored during the Qajar period.
Near the village of Bisotoun, in front of the mountain of the same name, about 38 kilometers north of Kermanshah, is the caravanserai called "of Sheikh Ali Khan Zanganeh", named after the governor of the area during the reign of Shah Abbas I Safavid the Great (1587 - 1628): in fact, when he became prime minister under the subsequent reign of Shah Soleiman, Sheikh Ali Khan donated some of the adjacent land to the community so that the profits from their cultivation were destined for the maintenance of the caravanserai. The plan of the structure, with four arcades, is very similar to that of Mahidasht, but at the four corners there are as many ornamental towers, and the central courtyard is rectangular (83,6 meters by 74,50). All around there are 47 rooms, in each of which the travelers of the various caravans were housed.