Middle Persian language in the context of "Gundeshapur"

The Sasanian Empire (/səˈsɑːniən/), 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 AD. Lasting for over four centuries, the length of the Sasanian dynasty's reign over ancient Iran was second only to that of the Arsacid dynasty of Parthia which immediately preceded it.

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 dominions of the Iranian nation. Most notably, after defeating Artabanus IV of Parthia at 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. These efforts by Sasanian rulers ultimately led to the re-establishment of Iran as a major power of late antiquity.

Angra Mainyu (/ˈæŋrə ˈmaɪnjuː/; Avestan: 𐬀𐬢𐬭𐬀⸱𐬨𐬀𐬌𐬥𐬌𐬌𐬎, romanized: Aŋra Maniiu) is the Avestan name of Zoroastrianism's hypostasis of the "destructive/evil spirit" and the main adversary in Zoroastrianism either of the Spenta Mainyu, the "holy/creative spirits/mentality", or directly of Ahura Mazda, the highest deity of Zoroastrianism. The Middle Persian equivalent is Ahriman (/ˈɑːrɪmən/; Middle Persian: 𐭠𐭧𐭫𐭬𐭭𐭩, romanized: Ahreman). The name can appear in English-language works as Ahrimanes.

Parthia (Old Persian: 𐎱𐎼𐎰𐎺 Parθava; Parthian: 𐭐𐭓𐭕𐭅 Parθaw; Middle Persian: 𐭯𐭫𐭮𐭥𐭡𐭥 Pahlaw) is a historical region located in northeastern Greater Iran. It was conquered and subjugated by the empire of the Medes during the 7th century BC, was incorporated into the subsequent Achaemenid Empire under Cyrus the Great in the 6th century BC, and formed part of the Hellenistic Seleucid Empire after the 4th-century BC conquests of Alexander the Great. The region later served as the political and cultural base of the Eastern Iranian Parni people and Arsacid dynasty, rulers of the Parthian Empire (247 BC – 224 AD). The Sasanian Empire, the last state of pre-Islamic Iran, also held the region and maintained the seven Parthian clans as part of their feudal aristocracy.

Kavad I (Middle Persian: 𐭪𐭥𐭠𐭲 Kawād; 473 – 13 September 531) was the Sasanian King of Kings of Iran from 488 to 531, including a two or three-year interruption. A son of Peroz I (r. 459–484), he was crowned by the nobles to replace his deposed and unpopular uncle Balash (r. 484–488).

Inheriting a declining empire where the authority and status of the Sasanian kings had largely weakened, Kavad tried to reorganize his empire by introducing many reforms whose implementation was completed by his son and successor, Khosrow I. They were made possible by Kavad's use of the Mazdakite preacher Mazdak, leading to a social revolution that weakened the authority of the nobility and the clergy. Because of this, and the execution of the powerful king-maker Sukhra, Kavad was deposed and imprisoned in the Castle of Oblivion. He was replaced by his brother Jamasp. However, with the aid of his sister and an officer named Siyawush, Kavad and some of his followers fled east to the territory of the Hephthalite king, who provided him with an army. This enabled Kavad to restore himself to the throne in 498/9.

Khosrow I (also spelled Khosrau, Khusro or Chosroes; Middle Persian: 𐭧𐭥𐭮𐭫𐭥𐭣𐭩), traditionally known by his epithet of Anushirvan (Middle Persian: 𐭠𐭭𐭥𐭱𐭫𐭥𐭡𐭠𐭭, lit. 'the Immortal Soul'), was the Sasanian King of Kings of Iran from 531 to 579. He was the son and successor of Kavad I (r. 488–496, 498/9–531).

Inheriting a reinvigorated empire at war with the Byzantines, Khosrow I signed a peace treaty with them in 532, known as the Perpetual Peace, in which the Byzantine emperor Justinian I paid 11,000 pounds of gold to the Sasanians. Khosrow then focused on consolidating his power, executing conspirators, including his uncle Bawi. Dissatisfied with the actions of the Byzantine clients and vassals, the Ghassanids, and encouraged by Ostrogoth envoys from Italy, Khosrow violated the peace treaty and declared war against the Byzantines in 540. He sacked the major city of Antioch and deported its population to Persia. In 541, he invaded Lazica and made it an Iranian protectorate, thus initiating the Lazic War. In 545, the two empires agreed to halt the wars in Mesopotamia and Syria while continuing to fight in Lazica. A truce was declared in 557, and by 562 the fifty-year peace treaty was signed.

Ctesiphon (/ˈtɛsɪfɒn/ TESS-if-on; Middle Persian: 𐭲𐭩𐭮𐭯𐭥𐭭, Tyspwn or Tysfwn; Persian: تیسفون; Ancient Greek: Κτησιφῶν, Attic Greek: [ktɛːsipʰɔ̂ːn]; Syriac: ܩܛܝܣܦܘܢ) was an ancient city in modern Iraq, on the eastern bank of the Tigris, about 35 kilometres (22 mi) southeast of Baghdad. Ctesiphon served as a royal capital of the Iranian empires for over eight hundred years, in the Parthian and Sasanian periods. Ctesiphon was the administrative capital of the Sasanian Empire from 226 to 637 (when it was conquered by the Arabs), or until the conclusion of the Muslim conquest of Persia in 651 AD.

Ctesiphon developed into a rich commercial metropolis, merging with the surrounding cities along both shores of the river, including the Hellenistic city of Seleucia. Ctesiphon and its environs were therefore sometimes referred to as "The Cities" (Mahuza, Arabic: المدائن, romanized: al-Mada'in). In the late 6th and early 7th century, it was listed as the largest city in the world by some accounts.

Arya (Avestan: 𐬀𐬌𐬭𐬌𐬌𐬀, airiia; Old Persian: 𐎠𐎼𐎡𐎹, ariyaʰ; Middle Persian: 𐭠𐭩𐭫‎, er; Parthian: 𐭀𐭓𐭉‎, ary; Bactrian: αρια, aria) was the ethnonym used by Iranians during the early History of Iran. In contrast to cognates of Arya used by the Vedic people and Iranic steppe nomads, the term is commonly translated using the modern ethnonym Iranian.

During Old Iranian times, the term was connected with one's lineage, with speaking an Iranian language and with the worship of Ahura Mazda. Being an Arya, therefore, had ethnic, linguistic and religious aspects. During the Middle Iranian period, it acquired a distinct political aspect through the concept of Eran Shahr (Aryas' dominion). Arya was also contrasted with Anarya (Avestan: 𐬀𐬥𐬀𐬌𐬭𐬌𐬌𐬀, anairiia; Middle Persian: 𐭠𐭭𐭩𐭥‎, aner), denoting non-Iranian lands and peoples.

Ardashir I (Middle Persian: 𐭠𐭥𐭲𐭧𐭱𐭲𐭥, romanized: Arda(x)šēr), also known as Ardashir the Unifier (180–242 AD), was the founder of the Sasanian Empire, the last empire of ancient Iran. After defeating the last Parthian shahanshah Artabanus IV on the Hormozdgan plain in 224, he overthrew the Arsacid dynasty and established the Sasanian dynasty. Afterwards, Ardashir called himself shahanshah and began conquering the land that he called Eranshahr, the realm of the Iranians.

There are various historical reports about Ardashir's lineage and ancestry. According to al-Tabari's History of the Prophets and Kings, Ardashir was son of Papak, son of Sasan. Another narrative recorded in Kar-Namag i Ardashir i Pabagan and Ferdowsi's Shahnameh states that Ardashir was born from the marriage of Sasan, a descendant of Darius III, with the daughter of Papak, a local governor in Pars.

Khorasan (Middle Persian: 𐬒𐬊𐬭𐬀𐬯𐬀𐬥, romanized: Xwarāsān; Persian: خراسان, Iranian Persian [xoɾɒːˈsɒːn] ) is a historical eastern region in the Iranian Plateau in West and Central Asia that encompasses western and northern Afghanistan, northeastern Iran, the eastern halves of Turkmenistan and Uzbekistan, western Tajikistan, and portions of Kyrgyzstan and Kazakhstan.

The extent of the region referred to as Khorasan varied over time. In its stricter historical sense, it comprised the present territories of northeastern Iran, parts of Afghanistan and southern parts of Central Asia, extending as far as the Amu Darya (Oxus) river. However, the name has often been used in a loose sense to include a wider region that included most of Transoxiana (encompassing Bukhara and Samarqand in present-day Uzbekistan), extended westward to the Caspian coast and to the Dasht-e Kavir southward to Sistan, and eastward to the Pamir Mountains. Greater Khorasan is today sometimes used to distinguish the larger historical region from the former Khorasan Province of Iran (1906–2004), which roughly encompassed the western portion of the historical Greater Khorasan.