The Sassanid Empire or Sassanian Dynasty (Persian: ساسانیانsɒsɒnijɒn]) is the name used for the fourth imperial Iranian dynasty, and the second Persian Empire (226–651). The Sassanid dynasty was founded by Ardashir I after defeating the last Parthian (Arsacid) king, Artabanus IV (Persian: اردوان Ardavan) and ended when the last Sassanid Shahanshah (King of Kings), Yazdegerd III (632–651), lost a 14-year struggle to drive out the early Islamic Caliphate, the first of the Islamic empires. The empire's territory encompassed all of today's Iran, Iraq, Armenia, Afghanistan, eastern parts of Turkey, and parts of India, Syria, Pakistan, Caucasia, Central Asia and Arabia. During Khosrau II's rule in 590–628 Egypt, Jordan, Palestine/Israel, Lebanon were also briefly annexed to the Empire. The Sassanids called their empire Eranshahr "Dominion of the Iranians (Aryans)". The Sassanid era, encompassing the length of the Late Antiquity period, is considered to be one of the most important and influential historical periods in Iran. In many ways the Sassanid period witnessed the highest achievement of Persian civilization, and constituted the last great Iranian Empire before the Muslim conquest and adoption of Islam. Persia influenced Roman civilization considerably during the Sassanids' times, and the Romans reserved for the Sassanid Persians alone the status of equals, exemplified in the letters written by the Roman Emperor to the Persian Shahanshah, which were addressed to "my brother." Their cultural influence extended far beyond the empire's territorial borders, reaching as far as Western Europe, Africa, China and India and played a prominent role in the formation of both European and Asiatic medieval art.
This influence carried forward to the early Islamic world. The dynasty's unique and aristocratic culture transformed the Islamic conquest of Iran into a Persian Renaissance. Much of what later became known as Islamic culture, architecture, writing and other skills, were taken mainly from the Sassanid Persians into the broader Muslim world. For instance, Afghanistan's official language, which is the Dari dialect of Persian, evolved from the royal language of the Sassanids.