In second half of the IV ^E century, at the time when, in Occident, Philippe II of Macedonia carries out the unit of Greece, the Empire achéménide is at the edge of the ruin. Alexandre the Large one, heir to Philippe, taking again the project of his father, launches a forwarding against Persians.

In 334 av. J. - C., the Empire crumbles in front of the phalanges Macedonians of Alexandre, who, in a few years, will push his conquest to Indus. However, contrary to any waiting, Alexandre behaves of legitimate heir to the defeated; following the example of Cyrus the Large one, it makes watch of the greatest tolerance towards its new subjects. Even, it takes again on its account the ceremonial of the court achéménide and gives its officers and its soldiers Macedonians of the Persian wives. However, it substitutes for the Aramaic the Greek koinè, which becomes the vehicle of communication of everyone Greek at the time Hellenistic; the Iranian children are educated besides in this language.

The attempt to link in the same empire the East and Occident, wish of Alexandre, crumbles with the untimely death of the Macedonian, in 323 av. J. - C. Nevertheless, the consequences of its conquests in Asia are very important on the cultural level, in particular the diffusion of the Hellenism, in particular in Iran.

After the division of the heritage of Alexandre between his generals, the diadoques ones, of vast territories extending from the Mediterranean in Indus - not understood Egypt, Palestine, southernmost Syria and part of the littoral of Minor Asia - fall to Séleucos, satrap Greek of Babylon. This one founds the Hellenistic dynasty of Séleucides and takes the name of Séleucos I ^er.

It tries to continue the policy of Alexandre by creating new cities - Séleucie on the Tiger, Antioche on Oronte - and by hellenizing the old Persian capitals: Suse becomes Séleucie, Ecbatane takes the name of Épiphanéia. However, the action séleucide encounters rather quickly a sharp opposition of Parthes arsacides.

The come to power of a dynasty of kings originating in Iran seems a national reaction to the Hellenistic influence. Parthes, of the nomads connected with the Scythians, emigrants of the area of the sea of Aral and the Caspian Sea, led by Arsace - which will give its name to the dynasty -, settle in Hyrcanie-Parthiène in second half of IIIe century.

Obstinate, they badger Séleucides; during IIe century, their king Mithridate I manages to take various provinces under domination séleucide, in particular Iran and Babylonia, where it founds the new Parthian capital, Ctésiphon, opposite Séleucie.

The Silk route

This new Empire, which extends from current Afghanistan in Euphrate, occupies a dominating place in the commercial relations between the Occident, the Indies and the Far East. Parthes, which maintains the close relationships with the Chinese, will control the Silk route; Iran becomes thus a turntable of the Eastern products bound for Mésopotamie, Syria and the Empire Roman, then main of most of the Middle East. The Romans seek to exceed the border of Euphrate and to take the control of Arménie, fallen under the Parthian dependence. At the end of a baited war, which extends on nearly three centuries, Parthes, weakened, end up yielding vis-a-vis Trajan in 115-117 apr. J. - C; in Lucius Verus in 165; and in Severe Septime in 197-198. It is the beginning of the decline of the Parthian royalty, which will be destroyed by Sassanides.

Parthes, before nomads, appeared large builders. Under their reign, Mésopotamie knows an intense urban activity; important restoration or building work is completed in Babylon, Ourouk, Kish, Séleucie, Nippour. In the same way, they made reappear the abandoned cities of Girsou (today Tello), Ninive and Assour.

On the cultural level, Parthian civilization does not mark a great rupture with the period séleucide. The employment of the Greek prevails, in spite of the adoption of the written Parthian language, from which the alphabet is derived from the Aramaic. On the currencies, where the gods represented are Greek, the kings arsacides carry the title of “Philhellènes”.

However, starting from I ^er century apr. J. - C., the rejection of the Hellenism starts to be felt: return to old Iranian religious traditions, multiplication, on the currencies, of legends in Parthian language, search of artistic forms and released techniques of all external influences, etc the day before the era sassanide, Iran is detached slowly from the Hellenistic influence.

At the beginning of the III ^E century, Ardachêr I, victorious of the Parthian king Artaban V, is made crown king with Ctésiphon towards 224. It founds the Persian Empire thus sassanide - whose name comes from Sassan, its eponymous ancestor -, who claimed to join again with the traditions achéménides.

Indeed, Sassanides are also Persians originating in Fars, but the renewal of the history stops there. Revolted against Parthes, they arrive, as of 224 apr. J. - C., to subject Babylonia and the capital of the Empire, Séleucie-Ctésiphon. In 241, at the time when king Ardachêr gives up the power, the Empire sassanide extends from Euphrate to the accesses of Indus.

Like their predecessors parthes, Sassanides seek to make sure control of the shopping streets between the Mediterranean, the Indies and the Far East; with this intention, they must fight on two faces; one Western, vis-a-vis Rome and soon in Byzance; the other Eastern one, vis-a-vis the empire of Kouchans and with the wandering powers of the Central Asia, Huns and Turks. Most kings sassanides give this double mission; the first succeed in gaining important victories over the Roman Emperors, but, starting from the IV ^E century, successes sassanides are done rarer.

With the O C century, inside the Empire, the plots of the nobility multiply and religious and social violence mazdakites develops, while the war begins again at its borders, in the west as in the east, vis-a-vis the Romans.

To the VI ^E century, however, the State sassanide knows a certain rectification: Khosrô Ier (Chosroès), which reached the power towards 531, restores the order inside while proceeding to reforms and while putting an end to the movement mazdakite, while at outside it signs peace with Byzance but destroys Huns; it extends its domination to Yemen, from where it drives out the Ethiopian ones (575).

Under Khosrô II, the Empire reaches its apogee; the war, in the Western part, shows important victories; the Persian troops occupy successively Arménie, Édesse, Césarée de Cappadoce, Antioche, Damas and Jerusalem. In 619, Khosrô II pushes through Egypt, where it occupies all Is and extends its influence to Alexandria. However, successes sassanides rather quickly appear transitory; as of 628, Byzance seizes again, recovers all its lost territories and besieges even Ctésiphon. From 634, Sassanides, weakened, undergo the Arab invasion. Their empire, less better structured than that of the Byzantines, is destroyed by the Arab expansion. They are defeated into 637 in Qadisiyya, close to Euphrate, and into 642 in Nehavend, and their empire passes under Islamic domination.

Culturally, the last empire, that of Sassanides, in particular under the reign of Chosroès, are detached from the Hellenistic and parthic traditions to join again with those of the time achéménide.