At the age of 16, he launched enormously successful military campaigns against Arab insurrections and tribes, who knew him as Dhu'l-Aktaf 'he who pierces shoulders'.

[1] When Hormizd II died in 309, he was succeeded by his son Adur Narseh, who, after a brief reign which lasted few months, was killed by some of the nobles of the empire.

The crowning of the infant Shapur after the elimination of his older brothers was a means for the nobility and priesthood to gain greater control of the empire.

[9] During the childhood of Shapur II, Arab nomads raided the Sasanian homeland of Pars, particularly the district of Ardashir-Khwarrah and the shore of the Persian Gulf.

[10] At the age of 16, Shapur II led an expedition against the Arabs; primarily campaigning against the Iyad tribe in Asoristan and thereafter he crossed the Persian Gulf, reaching al-Khatt, modern Qatif, or present eastern Saudi Arabia.

Shapur II reportedly killed a large number of the Arab population and destroyed their water supplies by stopping their wells with sand.

[14] The Lakhmid ruler Imru' al-Qays ibn 'Amr, who was originally a vassal of the Sasanians, may have suffered from Shapur II's raids in Peninsula.

[15] Ever since the "humiliating" Peace of Nisibis concluded between Shapur's grandfather Narseh and the Roman emperor Diocletian in 298, the borders between the two empires had changed largely in favor of the Romans, who in the treaty received a handful of provinces in Mesopotamia, changing the border from the Euphrates to the Tigris, close to the Sasanian capital of Ctesiphon.

[21][c] Neither side managed to achieve a decisive advantage, and an invasion of Central Asian nomads in the east forced Shapur to abandon his campaign against Rome by 350.

[24] In 356, Shapur rejected a peace overture by Constantius, replying that Rome should return Armenia and other territories lost by Persia in the Treaty of Nisibis.

In the next year Constantius II launched a counterattack, having spent the winter making massive preparations in Constantinople; Shapur, who had meanwhile lost the aid of his Asianic allies, avoided battle, but left strong garrisons in all the fortresses which he had captured.

Though Shapur attempted an honorable reconciliation, warned of the capabilities which Julian had displayed in wars against the Alemanni in Gaul, the emperor dismissed negotiation.

His successor Jovian (363–364) made an ignominious peace in which the districts beyond the Tigris which had been acquired in 298 were given to the Persians along with Nisibis and Singara, and the Romans promised to interfere no more in Armenia.

[10] The great success is represented in the rock sculptures near the town Bishapur in Pars (Stolze, Persepolis, p. 141); under the hooves of the king's horse lies the body of an enemy, probably Julian, and a supplicant Roman, the Emperor Jovian, asks for peace.

[29] The Persians were assisted in Armenia by the magnates Meruzhan Artsruni and Vahan Mamikonian, who were made governors of the country and one of whom was given Shapur's own sister in marriage.

[27][f] However, the Armenian nobles resisted him successfully, secretly supported by the Romans, who sent King Pap, the son of Arshak II, into Armenia.

[38] During the last phase of the reign of Shapur II, a Sasanian mint was established south of the Hindu Kush, the role of which was probably to pay local troops.

[38][39] In the area of Sindh, from Multan to the mouth of the Indus river, an important series of gold coins started to be issued on the model of the coinage of Shapur II, and would continue down to Peroz I.

Ammianus Marcellinus reports that in 356 CE, Shapur II was taking his winter quarters on his eastern borders, "repelling the hostilities of the bordering tribes" of the Chionites and the Euseni ("Euseni" is usually amended to "Cuseni", meaning the Kushans),[44] finally making a treaty of alliance with the Chionites and the Gelani in 358 CE.

From around 360 CE, however, during his reign, the Sasanids lost the control of Bactria to invaders from the north, first the Kidarites, then the Hephthalites and the Alchon Huns, who would follow up with the invasion of India.

[46] Various coins minted in Bactria and based on a Sasanian designs are known, often with busts imitating Sasanian kings Shapur II (r. 309 to 379 CE) and Shapur III (r. 383 to 388 CE), adding the Alchon Tamgha and the name "Alchono" in Bactrian script on the obverse, and with attendants to a fire altar on the reverse.

[48] At the time of Shapur's death, the Sasanian Empire was stronger than it had ever been, and it was also considerably larger than when he came to the throne, the eastern and western enemies were pacified and Persia had gained control over Armenia.

[49] Under Shapur II's reign, the collection of the Avesta was completed, heresy and apostasy punished, and the Christians persecuted (see Abdecalas, Acepsimas of Hnaita and Abda of Kashkar).

[51] Shapur's own religious beliefs do not seem to have been very strict; he restored the family cult of Anahita in Istakhr and was possibly an adherent of Zurvanism as well as promoting the official orthodox variant of Zoroastrianism.

[52] Initially, Shapur II was not hostile to his Christian subjects, who were led by Shemon Bar Sabbae, the Patriarch of the Church of the East.

After the death of Constantine, Shapur II, who had been preparing for a war against the Romans for several years, imposed a double tax on his Christian subjects to finance the conflict.

Sozomen estimates the total number of Christians killed as follows: The number of men and women whose names have been ascertained, and who were martyred at this period, has been computed to be upwards of sixteen thousand, while the multitude of martyrs whose names are unknown was so great that the Persians, the Syrians, and the inhabitants of Edessa, have failed in all their efforts to compute the number.According to Ammianus Marcellinus, Shapur II fought the Romans in order to "re-conquer what had belonged to his ancestor".