The way of establishing the Sasanian Empire like the story of Ardeshir, founder of this dynasty, is ambiguous. But according to the narrations, King Papak (King of Istakhr in current Fars province) dreamed while sleeping that experts interpreting that the Sasan’s son (the Shepherd of the King) would become the king of kings of the world. So Papak becomes his daughter to be Sassan’s wife, which Ardashir I is the result of this marriage. But some of the experts believe Sasan was also responsible for the fire temple of Anahita in the city. After Papak, Ardashir becomes the king of Istakhr then he killed Ardavan V (the last king of the Parthians) and overcomes other claimants, and announced himself as the King of the Kings of Iran. One of the most important achievements of Ardashir is invaded the eastern region of the Roman Empire and establish new cities and epigraphs.
After that Ardashir left his kingdom for his son, King Shapur became the Sassanid empire king. He tranquilizes turbulence in the eastern borders of the Sassanid empire with a battle and overcomes the Kushani empire. Then he became ready for involvement with the Romans. He captured Antioch, Valerin (Roman king), and 70,000 Roman soldiers. Hormizd I, Bahram I, Bahram II, Bahram III, Narseh, and the Hormizd II are from the other kings of the Sasanian Empire. One of the important events in the period of these kings was a couple of wars of the Sasanian Empire with the Roman Empire, which sassanids defeated in both of them and five provinces of Armenia fell to the Romans.
After years of incompetence, Shapur II sat on the throne. One of the important actions of Shapur II is the retardation of Arabs from Iran. He became famous because of piercing the shoulders of Arab captives, he has been nicknamed Zu-l-aktaf. Then the eastern tribesmen who had invaded Iran were also retard from Iran borders and then prepared for war with the Roman empire. In a war between the Sasanian Empire and Roman armies, ultimately, Julian was murdered by the Iranian, and his deputy, Jovian, was forced to step in peace with Shapur, thus all regions that had been taken from Iran in previous wars returned to the Sasanian Empire. In 379 AD, Shapur II, one of the greatest Sassanid kings, died. After him, the country suffered from a lot of problems that, over 100 years, all the kings of sassanids who sat on the throne were incompetent, the important events of this period are the division of Armenia between Iran and the Roman Empire, the eastern part for Iran, and the western part go to Rome.
After several corrupted kings, it was Khosrow I who became the king of the Sassanid empire. Khosrow I can be count as one of the greatest kings of Iran due to internal reforms and victories in overseas wars. He succeeded in eliminating eastern tribes by uniting with the Khagan of Turks, and after that Iranians have been neighbors with Turk tribes. Then in 572 AD, sent the navy to Yemen, this region was dominated by the Sasanian Empire. Khosrow I, later called Khosrow Anushiruwan, died in 579 AD, after 50 years of kingdom. After him, the struggle for the throne continued, and sometimes a king was killed and then he was deposed. Until the Yazdgerd’s crowned, struggles were over but a more fundamental problem was the Arab invasion of Iran.
After the death of the Prophet Muhammad, Muslims attacked the territories under the domination of the Romans and the Persians, and the result of these invasions was the Levant, Palestine, and Egypt, which was at the domination of the Roman Empire and the defeat of Persians in the war of al-Qadisiyyah. After the defeat of Iranians in this war, Yazdgerd III escaped to the eastern borders of Iran, where were killed by an unknown miller, thus Sasanian Empire finished by his death.