Sassanid Empire

The Sassanid Empire or Sasanian Dynasty is the name used for the Persian dynasty that lasted from 224 to 651 AD.
The Sassanid Empire, which succeeded the Parthian Empire, was recognised as one of the two great powers in Western Asia, alongside the Roman Empire and later the Byzantine Empire, for more than 400 years.
King of kings
The Sassanid dynasty was founded by Ardashir I when he defeated the last Parthian (Arsacid) king, Artabanus IV, and ended when the last Sassanid Shahanshah (King of Kings), Yazdegerd III (632-651), lost a fourteen-year struggle to drive out the early Arab Caliphate, the first of the Islamic empires.
The Sassanid Empire's traditional territory included what is now Iran, Iraq, Armenia, Afghanistan, Egypt and eastern Turkey and parts of Syria, Pakistan, Caucasia, Central Asia and Arabia.
The Sassanid era is considered to be one of the most important and influential historical periods in Iran. In many ways; the Sassanid period saw the highest achievement of Persian civilization, and was the last great Persian Empire before the Muslim conquest and the adoption of Islam.
Persia influenced Roman civilization considerably during the Sassanids,p109 and the Romans reserved for the Sassanid Persians the status of equals. The Roman Emperor wrote letters to the Persian Shahanshah, which were addressed to "my brother". Their cultural influence extended far beyond the empire's territorial borders by reaching as far as Western Europe, Africa, China and India and played a prominent role in the formation of both European and Asiatic mediaeval art.
This influence carried forward to the early Islamic world. The dynasty's unique aristocratic culture transformed the Islamic conquest of Iran into a Persian renaissance. Much of what later became known as Islamic culture, architecture, writing andother skills were borrowed from the Sassanid Persians and spead throughout the broader Muslim world.
Decline
In the spring of 632, a grandson of Khosrau I, Yazdegerd III, who had lived in hiding, ascended the throne. The same year, the first raiders from the Arab tribes made their raids into Persian territory. They were united by Islam. Years of warfare had exhausted both the Byzantines and the Persians. Also, the latter were further weakened by economic decline, heavy taxation, religious unrest, rigid social classes, the increasing power of the provincial landholders and a rapid turnover of rulers. Those factors made the Islamic conquest of Persia easier than if it had been attempted earlier.
The Sassanids never mounted a truly effective resistance to the pressure that was applied by the Muslim conquests.
Sassanid Empire chronology
226-241: Reign of Ardashir I:
224-226: Overthrow of Parthian Empire.
229-232: War with Rome.
Zoroastrianism is revived as official religion.
The collection of texts known as the Zend Avesta is assembled.
241-271: Reign of Shapur I:
241-244: War with Rome.
252-261: War with Rome. Capture of Roman emperor Valerian.
215-271: Mani, founder of Manichaeism.
271-301: A period of dynastic struggles.
283: War with Rome. Romans sack Ctesiphon.
296-8: War with Rome. Persia cedes five provinces east of the Tigris to Rome.
309-379: Reign of Shapur II "the Great":
337-350: First war with Rome with relatively little success.
359-363: Second war with Rome. Rome returns trans-Tigris provinces and cedes Nisibis and Singara to Persia.
387: Armenia partitioned into Roman and Persian zones.
399-420: Reign of Yazdegerd I "the Sinner":
409: Christians are permitted to publicly worship and to build churches.
416-420: Persecution of Christians as Yazdegerd revokes his earlier order.
420-438: Reign of Bahram V:
420-422: War with Rome.
424: Council of Dad-Ishu declares the Eastern Church independent of Constantinople.
428: Persian zone of Armenia annexed to Sassanid Empire.
438-457: Reign of Yazdegerd II:
441: War with Rome.
449-451: Armenian revolt.
482-3: Armenian and Iberian revolt.
483: Edict of Toleration granted to Christians.
484: Peroz I defeated and killed by Hephthalites.
491: Armenian revolt. Armenian Church repudiates the Council of Chalcedon:
Nestorian Christianity becomes dominant Christian sect in Sassanid Empire.