Flag of the Sasanian Empire (Derafsh Kavian), Iran Aufkleber

The Sasanian Empire (/səˈsɑːniən, səˈseɪniən/), officially Eranshahr (Middle Persian: 𐭠𐭩𐭥𐭠𐭭𐭱𐭲𐭥𐭩 Ērānšahr, "Empire of the Iranians"), was an Iranian empire that was founded and ruled by the House of Sasan from 224 to 651. Enduring for over four centuries, the length of the Sasanian dynasty's reign over ancient Iran was second only to the directly preceding Arsacid dynasty of Parthia. Founded by Ardashir I, whose rise coincided with the decline of Arsacid influence in the face of both internal and external strife, the House of Sasan was highly determined to restore the legacy of the Achaemenid Empire by expanding and consolidating the Iranian nation's dominions. Most notably, after defeating Artabanus IV of Parthia during the Battle of Hormozdgan in 224, it began competing far more zealously with the neighbouring Roman Empire than the Arsacids had, thus sparking a new phase of the Roman–Iranian Wars. This effort by Ardashir's dynasty ultimately re-established Iran as a major power of late antiquity. At their zenith, the Sasanians controlled all of modern-day Iran and Iraq and parts of the Arabian Peninsula (particularly Eastern Arabia and South Arabia), as well as the Caucasus, the Levant, and parts of Central Asia and South Asia. They maintained Ctesiphon as the capital city—as it had been under the Arsacids—for all but the first two years of their empire's existence, when Istakhr briefly served in this capacity. One of the high points in the history of Iranian civilization, the Sasanian Empire was characterized by a complex and centralized government bureaucracy and the revitalization of Zoroastrianism as a legitimizing and unifying ideal. This period saw the construction of many grand monuments, public works, and patronized cultural and educational institutions. Under the Sasanians, Iran's cultural influence spread far beyond the physical territory that it controlled, impacting regions as distant as Western Europe, Eastern Africa, and China and India. It also helped shape European and Asian medieval art. Following the rise of Islam in Arabia, the Sasanian Empire capitulated to the early Muslim conquests, which were initiated by Muhammad and continued by the Rashidun Caliphate. Although the Muslim conquest of Iran marked a significant religious and cultural shift in the nation's history, the Islamization of Iran enabled the gradual absorption of Sasanian art, architecture, music, literature, and philosophy into nascent Islamic culture, which, in turn, ensured and sustained the proliferation of evolving Iranian culture, knowledge, and ideas throughout the growing Muslim world.