Shapur I (also spelled Shabuhr I; ) also known as Shapur I the Great was the second Sasanian King of Kings of Iran. The precise dating of his reign is disputed, but it is generally agreed that he ruled from 240 to 270, with his father Ardashir I as co-regent until the death of the latter in 242. Shapur also consolidated and expanded the empire of Ardashir I, waged war against the Roman Empire, and seized its cities of Nisibis and Carrhae while he was advancing as far as Roman Syria. Although he was defeated at the Battle of Resaena in 243 by Roman emperor Gordian III (), the following year he was able to win the Battle of Misiche and force the new Roman emperor Philip the Arab () to sign a favorable peace treaty that was regarded by the Romans as "a most shameful treaty".

Shapur later took advantage of the political turmoil within the Roman Empire by undertaking a second expedition against it in 252/3–256, sacking the cities of Antioch and Dura-Europos. In 260, during his third campaign, he defeated and captured the Roman emperor, Valerian. He did not seem interested in permanently occupying the Roman provinces, choosing instead to resort to plundering and pillaging, gaining vast amounts of riches. The captives of Antioch, for example, were allocated to the newly reconstructed city of Gundeshapur, later famous as a center of scholarship. In the 260s, subordinates of Shapur suffered setbacks against Odaenathus, the king of Palmyra. According to Shapur's inscription at Hajiabad, he still remained active at the court in his later years, participating in archery. He died of illness in Bishapur, most likely in May 270.

Shapur was the first Iranian monarch to use the title of "King of Kings of Iranians and non-Iranians"; beforehand the royal titulary had been "King of Kings of Iranians". He had adopted the title due to the influx of Roman subjects whom he had deported during his campaigns. However, it was first under his son and successor Hormizd I, that the title became regularized. Shapur had new Zoroastrian fire temples constructed, incorporated new elements into the faith from Greek and Indian sources, and conducted an extensive program of rebuilding and refounding of cities. He was also tolerant of Manichaeism, a new religious movement founded during his time by the prophet Mani.

Name Shapur was a popular name in Sasanian Iran, being used by three Sasanian monarchs and other notables during and after the Sasanian era. Derived from Old Iranian * 'son of a king', it must initially have been a title, which became—at least in the late 2nd century AD—a personal name. It appears in the list of Arsacid kings in some Arabic-Persian sources; however, this is anachronistic. Shapur is transliterated in other languages as; Greek , and ; Latin and ; Arabic and ; New Persian , , .

Birth According to the semi-legendary Kar-Namag i Ardashir i Pabagan, a Middle Persian biography of Ardashir I, the daughter of the Parthian king Artabanus IV, Zijanak, attempted to poison her husband Ardashir. Discovering her intentions, Ardashir ordered her to be executed. Finding out about her pregnancy, the mobads (priests) were against it. Nevertheless, Ardashir still demanded her execution, which led the mobads to conceal her and her son Shapur for seven years, until the latter was identified by Ardashir, who chose to adopt him based on his virtuous traits. This type of narrative is repeated in Iranian historiography. According to 5th-century BCE Greek historian Herodotus, the Median king Astyages wanted to have his grandson Cyrus killed because he believed that he would one day overthrow him. A similar narrative is also found in the story of the mythological Iranian king Kay Khosrow. According to the modern historian Michael Bonner, this story of Shapur's birth "may conceal a marriage between Ardashir and an Arsacid princess or perhaps merely a noble lady connected with the Parthian aristocracy." According to A. Shapur Shahbazi, this is one of several stories meant to legitimize Sasanian role by connecting Ardashir and his successors with the Parthian nobility. In the tale, the birth of Shapur to Zijanak takes place after the overthrow of Artabanus, but C. E. Bosworth states that Shapur I must have been born "well before" this event (i.e., before 224); the Sasanian rock reliefs and the history of al-Tabari indicate that Shapur took part in Ardashir's battles against the Parthians. In his inscriptions, Shapur identifies his mother as a certain Murrod.

Background and state of Iran Shapur I was a son of Ardashir I and his wife MurrodShahbazi, A. Shapur (2002). "Šāpur I". Encyclopaedia Iranica.Brosius, Maria (2000). "Women i. In Pre-Islamic Persia". Encyclopaedia Iranica, Vol. London et al.Bonner, Michael (2020). The Last Empire of Iran. New York: Gorgias Press. pp. 1–406. or Denag. The background of the Sasanian family is obscure; although based in Pars (also known as Persis), they were not native to the area, and were seemingly originally from the east. The historian Marek Jan Olbrycht has suggested that the family was descended from the Indo-Parthians of Sakastan. Iranologist Khodadad Rezakhani also noted similarities between the early Sasanians and the Indo-Parthians, such as their coinage. Yet, he stated that "evidence might still be too inconclusive."

Pars, a region in the southwestern Iranian plateau, was the homeland of the southwestern branch of the Iranian peoples, the Persians. It was also the birthplace of the first Iranian Empire, the Achaemenids. The region served as the center of the empire until its conquest by the Macedonian king Alexander the Great (). Since the end of the 3rd or the beginning of the 2nd century BCE, Pars was ruled by local dynasts subject to the Hellenistic Seleucid Empire. These dynasts held the ancient Persian title of frataraka ("leader, governor, forerunner"), which is also attested in the Achaemenid-era. Later under the frataraka Wadfradad II (fl. 138 BCE) was made a vassal of the Iranian Parthian (Arsacid) Empire. The frataraka were shortly afterwards replaced by the Kings of Persis, most likely at the accession of the Arsacid monarch Phraates II (). Unlike the fratarakas, the Kings of Persis used the title of shah ("king"), and laid foundations to a new dynasty, which may be labelled the Darayanids.

Under Vologases V (), the Parthian Empire was in decline, due to wars with the Romans, civil wars and regional revolts. The Roman emperor Septimius Severus () had invaded the Parthian domains in 196, and two years later did the same, this time sacking the Parthian capital of Ctesiphon. At the same time, revolts occurred in Media and Persis. The Iranologist Touraj Daryaee argues that the reign of Vologases V was "the turning point in Parthian history, in that the dynasty lost much of its prestige." The kings of Persis were now unable to depend on their weakened Parthian overlords. Indeed, in 205/6, Pabag rebelled and overthrew the Bazrangid ruler of Persis, Gochihr, taking Istakhr for himself. Around 208 Vologases VI succeeded his father Vologases V as king of the Arsacid Empire. He ruled as the uncontested king from 208 to 213, but afterwards fell into a dynastic struggle with his brother Artabanus IV, who by 216 was in control of most of the empire, even being acknowledged as the supreme ruler by the Roman Empire. Artabanus IV soon clashed with the Roman emperor Caracalla, whose forces he managed to contain at Nisibis in 217.

Peace was made between the two empires the following year, with the Arsacids keeping most of Mesopotamia. However, Artabanus IV still had to deal with his brother Vologases VI, who continued to mint coins and challenge him. The Sasanian family had meanwhile quickly risen to prominence in Pars, and had now under Ardashir begun to conquer the neighboring regions and more far territories, such as Kirman. At first, Ardashir I's activities did not alarm Artabanus IV, until later, when the Arsacid king finally chose to confront him.

Early life and co-rule

Shapur, as portrayed in the Sasanian rock reliefs, took part in his father's war with the Arsacids, including the Battle of Hormozdgan. The battle was fought on 28 April 224, with Artabanus IV being defeated and killed, marking the end of the Arsacid era and the start of 427 years of Sasanian rule. The chief secretary of the deceased Arsacid king, Dad-windad, was afterwards executed by Ardashir I. Ardashir celebrated his victory by having two rock reliefs sculptured at the Sasanian royal city of Ardashir-Khwarrah (present-day Firuzabad) in Pars. The first relief portrays three scenes of personal fighting; starting from the left, a Persian aristocrat seizing a Parthian soldier; Shapur impaling the Parthian minister Dad-windad with his lance; and Ardashir I ousting Artabanus IV. The second relief, conceivably intended to portray the aftermath of the battle, displays the triumphant Ardashir I being given the badge of kingship over a fire shrine from the Zoroastrian supreme god Ahura Mazda, while Shapur and two other princes are watching from behind. Ardashir considered Shapur "the gentlest, wisest, bravest and ablest of all his children" and nominated him as his successor in a council amongst the magnates. Shapur was crowned co-ruler of the empire on 12 April 240. He may have been crowned again as sole ruler in 243, but Richard N. Frye writes that a single coronation in 240 is more likely.

Military career

The eastern front

The eastern provinces of the fledgling Sasanian Empire bordered on the land of the Kushans and the land of the Sakas (roughly today's Turkmenistan, Afghanistan and Pakistan). The military operations of Shapur's father Ardashir I had led to the local Kushan and Saka kings offering tribute to the Sasanians. Satisfied by this show of submission, Ardashir seems to have refrained from occupying their territories. Al-Tabari alleges that he rebuilt the ancient city of Zrang in Sakastan (the land of the Sakas, Sistan), but the only founding of a new Sasanian settlement in the east which is certain in this period is the building by Shapur I of Nishapur—"Beautiful (city built) by Shapur"—in Dihistan (former Parthia, apparently lost by the Parthians to the Kushans).Thaalibi 485–486 even ascribes the founding of Badghis and Khwarazm to Ardashir I

Soon after the death of his father in 241 AD, Shapur felt the need to cut short the campaign they had started in Roman Syria and reassert Sasanian authority in the East, perhaps because the Kushan and Saka kings were lax in abiding by their tributary status. However, he first had to fight "The Medes of the Mountains"—possibly in the mountain range of Gilan on the Caspian coast—and after subjugating them, he appointed his son Bahram (the later Bahram I) as their king. He then marched to the East and annexed most of the land of the Kushans, and appointing his son Narseh as Sakanshah—king of the Sakas—in Sistan. In 242 AD, Shapur conquered khwarezm.Frye, Richard N. (1983). "The political history of Iran under the Sasanians". The Cambridge History of Iran: The Seleucid, Parthian, and Sasanian periods (1). Cambridge: Cambridge University Press. pp. 116–181. . Shapur could now proudly proclaim that his empire stretched all the way to Peshawar, and his relief in Rag-i-Bibi in present-day Afghanistan confirms this claim.W. Soward, "The Inscription of Shapur I at Naqsh-E Rustam in Fars", sasanika.org, 3.Cf. F. Grenet, J. Lee, P. Martinez, F. Ory, "The Sasanian Relief at Rag-i Bibi (Northern Afghanistan)” in G. Hermann, J. Cribb (ed.), After Alexander. Central Asia before Islam (London 2007), pp. 259–260 Shapur I claims in his Naqsh-e Rostam inscription possession of the territory of the Kushans () as far as "Purushapura" (Peshawar), suggesting he controlled Bactria and areas as far as the Hindu-Kush or even south of it: