Sasanian Empire in the context of "Armenia"

Late antiquity is a period of time that comes after the end of classical antiquity and stretches into the beginning of the Early Middle Ages, though the exact start and end dates are debated. Late antiquity represents a cultural sphere covering much of the Mediterranean world, including parts of Europe and the Near East.

Late antiquity was an era of massive political and religious transformation. Religiously, it marked the origins or ascendance of the three major monotheistic religions: Christianity, rabbinic Judaism, and Islam, as well as the period when both the Bible and the Quran were canonized. Politically, it marked the ends of the Western Roman Empire and the Sasanian Empire (the last Persian empire of antiquity), as well as the beginning of the Arab conquests and the formation of the Rashidun Caliphate. Meanwhile, the Byzantine Empire became a militarized and Christianized society. Late antiquity was also an era of significant cultural innovation and transformation, marked by the emergence of public architecture like the Hagia Sophia, and the emergence of late antique literature and art.

Iran, officially the Islamic Republic of Iran and also known as Persia, is a country in West Asia. It borders Iraq to the west, Turkey, Azerbaijan, and Armenia to the northwest, the Caspian Sea to the north, Turkmenistan to the northeast, Afghanistan to the east, Pakistan to the southeast, and the Gulf of Oman and the Persian Gulf to the south. With a population of over 90 million, Iran ranks 17th globally in both geographic size and population and is the sixth-largest country in Asia. Iran is divided into five regions with 31 provinces. Tehran is the nation's capital, largest city, and financial center.

Home to one of the world's oldest continuous major civilizations, most of Iran was first united as a nation by the Medes under Cyaxares in the 7th century BC and reached its territorial height in the 6th century BC, when Cyrus the Great founded the Achaemenid Empire. Alexander the Great conquered the empire in the 4th century BC. An Iranian rebellion in the 3rd century BC established the Parthian Empire, which later liberated the country. In the 3rd century CE, the Parthians were succeeded by the Sasanian Empire, who oversaw a golden age in the history of Iranian civilization. During this period, ancient Iran saw some of the earliest developments of writing, agriculture, urbanization, religion, and administration. Once a center for Zoroastrianism, the 7th century CE Muslim conquest brought about the Islamization of Iran. Innovations in literature, philosophy, mathematics, medicine, astronomy and art were renewed during the Islamic Golden Age and Iranian Intermezzo, a period during which Iranian Muslim dynasties ended Arab rule and revived the Persian language. This era was followed by Seljuk and Khwarazmian rule, Mongol conquests and the Timurid Renaissance from the 11th to 14th centuries.

The Middle East, or the Near East, was one of the cradles of civilization: after the Neolithic Revolution and the adoption of agriculture, many of the world's oldest cultures and civilizations were created there. Since ancient times, the Middle East has had several lingua franca: Akkadian, Hebrew, Aramaic, Greek, and Arabic. The Sumerians, around the 5th millennium BC, were among the first to develop a civilization. By 3150 BC, Egyptian civilization unified under its first pharaoh. Mesopotamia hosted powerful empires, notably Assyria which lasted for 1,500 years. For centuries after the 7th century BC, the region was dominated by Persian powers like the Achaemenid Empire.

In the 1st century BC, the Roman Republic conquered most of the region, and its successor, the Roman Empire, that ruled from the 6th to 15th centuries AD referred to as the Byzantine Empire, grew significantly more. Roman pagan religions were replaced by Christianity in the 4th century AD. From the 3rd to 7th centuries, Rome ruled alongside the Sasanian Empire. From the 7th century, Islam spread rapidly, expanding Arab identity in the region. The Seljuk dynasty displaced Arab dominance in the 11th century, followed by the Mongol Empire in the 13th century.

Constantine I (27 February 272 – 22 May 337), also known as Constantine the Great, or known mononymously as Constantine, was Roman emperor from AD 306 to 337 and the first Roman emperor to convert to Christianity. He played a pivotal role in elevating the status of Christianity in Rome, the Edict of Milan decriminalising Christian practice and ceasing Christian persecution. This was a turning point in the Christianisation of the Roman Empire. He founded the city of Constantinople (now Istanbul) and made it the capital of the Empire, which it remained for over a millennium.

Born in Naissus, a city located in the province of Moesia Superior (now Niš, Serbia), Constantine was the son of Flavius Constantius, a Roman army officer from Moesia Superior, who would become one of the four emperors of the Tetrarchy. His mother, Helena, was a woman of low birth, probably from Bithynia. Later canonised as a saint, she is credited for the conversion of her son in some traditions, though others believe that Constantine converted her. He served with distinction under emperors Diocletian and Galerius. He began his career by campaigning in the eastern provinces against the Persians, before being recalled to the west in AD 305 to fight with his father in the province of Britannia. After his father's death in 306, Constantine was proclaimed as augustus (emperor) by his army at Eboracum (York, England). He eventually emerged victorious in Civil wars of the Tetrarchy against the emperors Maxentius and Licinius to become the sole ruler of the Roman Empire by 324.

Theodosius I (Ancient Greek: Θεοδόσιος Theodosios; 11 January 347 – 17 January 395), also known as Theodosius the Great, was Roman emperor from 379 to 395. He won two civil wars and was instrumental in establishing the Nicene Creed as the orthodox doctrine for Nicene Christianity. Theodosius was the last emperor to rule the entire Roman Empire before its administration was permanently split between the Western Roman Empire and the Eastern Roman Empire. He ended the Gothic War (376–382), but did so on terms disadvantageous to the empire, with the Goths remaining and politically autonomous within Roman territory, albeit as nominal allies.

Born in Hispania, Theodosius was the son of a high-ranking general of the same name, Theodosius the Elder, under whose guidance he rose through the ranks of the Roman army. Theodosius held independent command in Moesia in 374, where he had some success against the invading Sarmatians. Not long afterwards, he was forced into retirement, and his father was executed under obscure circumstances. Theodosius soon regained his position following a series of intrigues and executions at Emperor Gratian's court. In 379, after the eastern Roman emperor Valens was killed at the Battle of Adrianople against the Goths, Gratian appointed Theodosius as a successor with orders to take charge of the military emergency. The new emperor's resources and depleted armies were not sufficient to drive the invaders out; in 382 the Goths were allowed to settle south of the Danube as autonomous allies of the empire. In 386, Theodosius signed a treaty with the Sasanian Empire which partitioned the long-disputed Kingdom of Armenia and secured a durable peace between the two powers.

The early Muslim conquests or early Islamic conquests (Arabic: الْفُتُوحَاتُ الإسْلَامِيَّة, romanized: al-Futūḥāt al-ʾIslāmiyya), also known as the Arab conquests, were a series of wars initiated in the 7th century by Muhammad, the prophet of Islam. He established the first Islamic state in Medina, Arabia that expanded rapidly under the Rashidun Caliphate and the Umayyad Caliphate, culminating in Muslim rule being established in Asia, Northern Africa, and Southern Europe over the following century. According to historian James Buchan: "In speed and extent, the first Arab conquests were matched only by those of Alexander the Great, and they were more lasting." At their height, the territory that was conquered by the Arab Muslims stretched from Iberia (at the Pyrenees) in the west to India (at Sind) in the east; Muslim control spanned Sicily, most of the Middle East and North Africa, and the Caucasus and Central Asia.

Among other drastic changes, the early Muslim conquests brought about the collapse of the Sasanian Empire and great territorial losses for the Byzantine Empire. Explanations for the Muslim victories have been difficult to discover, primarily because only fragmentary sources have survived from the period. American scholar Fred McGraw Donner suggests that Muhammad's establishment of an Islamic state in Arabia coupled with ideological (i.e., religious) coherence and mobilization constituted the main factor that propelled the early Muslim armies to successfully establish, in the timespan of roughly a century, one of the largest empires in history. Estimates of the total area of the combined territory held by the early Muslim polities at the conquests' peak have been as high as 13,000,000 square kilometres (5,000,000 sq mi). Most historians also agree that, as another primary factor determining the early Muslim conquests' success, the Sasanians and the Byzantines were militarily and economically exhausted from decades of warfare against each other.

Zoroastrianism, also called Mazdayasna or Behdin, is an Iranian religion centred on the Avesta and the teachings of Zarathushtra Spitama, who is more commonly referred to by the Greek translation, Zoroaster (Greek: Ζωροάστρις Zōroastris). Among the world's oldest organized faiths, its adherents exalt an uncreated, benevolent, and all-wise deity known as Ahura Mazda (𐬀𐬵𐬎𐬭𐬀⸱𐬨𐬀𐬰𐬛𐬁), who is hailed as the supreme being of the universe. Opposed to Ahura Mazda is Angra Mainyu (𐬀𐬢𐬭𐬀⸱𐬨𐬀𐬌𐬥𐬌𐬌𐬎), who is personified as a destructive spirit and the adversary of all things that are good. As such, the Zoroastrian religion combines a dualistic cosmology of good and evil with an eschatological outlook predicting the ultimate triumph of Ahura Mazda over evil. Opinions vary among scholars as to whether Zoroastrianism is monotheistic, polytheistic, henotheistic, or a combination of all three. Zoroastrianism shaped Iranian culture and history, while scholars differ on whether it significantly influenced ancient Western philosophy and the Abrahamic religions, or gradually reconciled with other religions and traditions, such as Christianity and Islam.

Originating from Zoroaster's reforms of the ancient Iranian religion, Zoroastrianism began during the Avestan period (possibly as early as the 2nd millennium BCE), but was first recorded in the mid-6th century BCE. For the following millennium, it was the official religion of successive Iranian polities, beginning with the Achaemenid Empire, which formalized and institutionalized many of its tenets and rituals, and ending with the Sasanian Empire, which revitalized the faith and standardized its teachings. In the 7th century CE, the rise of Islam and the ensuing Muslim conquest of Iran marked the beginning of the decline of Zoroastrianism. The persecution of Zoroastrians by the early Muslims in the nascent Rashidun Caliphate prompted much of the community to migrate to the Indian subcontinent, where they were granted asylum and became the progenitors of today's Parsis. Once numbering in the millions, the world's total Zoroastrian population is estimated to comprise between 110,000 and 120,000 people, with most of them residing either in India (50,000–60,000), in Iran (15,000–25,000), or in North America (22,000). The religion is thought to be declining due to restrictions on conversion, strict endogamy, and low birth rates.

Justinian I (Latin: Iustinianus, Ancient Greek: Ἰουστινιανός, romanized: Ioustinianós; 482 – 14 November 565), also known as Justinian the Great, was Roman emperor from 527 to 565.

His reign was marked by the ambitious but only partly realized renovatio imperii, or "restoration of the Empire". This ambition was expressed by the partial recovery of the territories of the defunct Western Roman Empire. His general, Belisarius, swiftly conquered the Vandal Kingdom in North Africa. Subsequently, Belisarius, Narses, and other generals conquered the Ostrogothic Kingdom, restoring Dalmatia, Sicily, Italy, and Rome to the empire after more than half a century of rule by the Ostrogoths. The praetorian prefect Liberius reclaimed the south of the Iberian Peninsula, establishing the province of Spania. These campaigns re-established Roman control over the western Mediterranean, increasing the Empire's annual revenue by over a million solidi. During his reign, Justinian also subdued the Tzani, a people on the east coast of the Black Sea that had never been under Roman rule before. He engaged the Sasanian Empire in the east during Kavad I's reign, and later again during Khosrow I's reign; this second conflict was partially initiated due to his ambitions in the west.