In 224 there was a controversy between the Parthians leaders for the throne, which was exploited by the younger son of a submissive local king, named Ardashir, who proclaimed himself as a king in Ctesiphon. He easily stabilized his power in the southern regions and with repeatedly bloody clashes with local rulers he succeeded in spreading his sovereign throughout the country. He eventually overthrew the Parthians' dynasty and replaced it with the Sassanid’s’ (from his father name that was Sassan), which will last for 400 years. Ardasir expanded the empire from the Euphrates to Afghanistan and to the south until Bahrain and the city of Mosul. His successor Sapur captured Mesopotamia and part of Syria, and in 260 he defeated the Romans in Edessa, capturing Emperor Valerian and 70,000 soldiers. The Romans counterattack occurred in 298 when Emperor Diocletian defeated Sassanid’s’ army and set the Tigris River as the border. VRAHOGRAPHY THAT DEPICTS ARDASIR ON HIS HORSE AND THE VALERIAN ON HIS KNEES
The Sassanid had developed a very powerful army with a spear tip the heavy cavalry, recruited by the landowners and the nobles of the provinces. Each feudal lord had to provide a certain amount of horsemen to the army from his jurisdiction and equip them at his own expense. The Romans called them horsemen of the blatant type because they had armor both on themselves and on their horses. The Iranian horses were strong enough to withstand the weight of the overall armor. The heirs of every feudal lord, if they wanted to preserve the ancestral clergy, had to serve in the cavalry with their people.

Sassanid’s official religion was the Zoroastrianism inherited by the Persians of the Achaemenid dynasty; their wizards had gained a great deal of power: providing justice, exercising public administration, and supervising the rulers of the empire with the help of a spy network. One of the wizards, named Tansar, circulated the scattered texts of Zoroastrianism and set up Avesta, the bible of the religion. The social stratification was as follows: King, clergy (priests-wizards), Army, Doctors, poets, astronomers, accountants, employees, technicians, merchants, growers, slaves.

The Sassanid dynasty, and the Zoroastrianism in Persia, ended in 651 when the country was conquered by the Arabs. The people were tired of the wars with Byzantium, the high taxes, the rigid social structure and the religious oppression, so they enthusiastically embraced the new religion, Islamism, that the Arabs brought with them.