By the onset of Sassanian rule in the early third century CE, Iranian maritime technology had resulted in the construction of vessels capable of transporting larger amounts of cargo over greater travel distances. Ardashir I was keen to establish military control over the Persian Gulf to dominate that region’s trade routes. This is corroborated by Islamic-era historians such as Thalabi, Hamza of Isfahan and Tabari, who record that Ardashir founded at least eight port cities. Note that these included ports established in the major waterways of Sassanianruled Mesopotamia and Khuzestan. The identified riverside ports include Bahman Ardashir (Forat of Maisan), Astarabadh Ardashir (former Charax), and Wahasht Ardashir, with ports on the Persian Gulf itself including locales such as Rev Ardashir (on the Bushehr Peninsula) and Kujeran Ardashir (probably opposite Kish), and Batn Ardashir (along the Arabian coast of the Persian Gulf opposite Bahrain island). The Karnamye Ardashir e Babakan provides a detailed account of the military campaign which Ardashir I fought to secure Kujaran. This success allowed the Sassanian military to effect naval landings in Bahrain as well as opposite Bahrain along the Arabian coast to subjugate the local tribes ensconced there. Ardashir I is then reported as having recruited Arab seafarers as advisors for building the Sassanian navy. Sassanian ships were known as kashtig (modern Persian: kashti) with the leader of the navy known as the navbad.
The empire’s main venue for seaborne commerce was the Persian Gulf and from there into the Indian Ocean and (by late Sassanian times) beyond into the Pacific Ocean and to China. Overseas trade was a major source of revenue for the empire, especially from the reign of Khosrow I. It resulted in the founding of a number of coastal cities along the Persian Gulf coast, from the modern-day Shaat al Arab/Arvand Rud waterway ingress in the west to the shores of modern-day Pakistan to the east. As hypothesized by Curatola and Scarcia, ‘these were fortified way stations along the coast controlled by the Persians’. The domain of studies pertaining to Sassanian coastal defences, however, is in progress at the time of writing. Nevertheless excavations thus far have provided great insight. Researchers generally agree that Sassanian coastal structures were intended to both accommodate commercial shipping and to also defend against seaborne attacks and attempted landings by hostile forces.
The vast majority of seaborne threats against the Sassanian Persian Gulf coastline were posed by Arab seaborne raiders emanating from the southern shores of the Persian Gulf in Arabia. The Arabs posed critical challenges to Iran’s military position in the Persian Gulf region and the south during the early years of Shapur II’s reign (310–379 CE). Driven by economic poverty and famine, Arab tribes from Hajar and Bahrain streamed across the Persian Gulf to attack and plunder the entire southern Iranian coastline from Khuzestan to the port city of Rev Ardashir. According to the Bundahishn, ‘in the reign of Shapur son of Hormuzd, the Arabs came and seized the banks of the River Karun (Ulay) and remained there for many years pillaging and attacking’. Southern coastal regions such as Rev Ardashir, for example, were plundered by Arab raiders who had arrived from the southern regions of the Persian Gulf. These attacks were viewed with special alarm by the spah, which assembled, under Shapur II’s leadership, a striking force at Gur. This army then boarded ships at ports along the Persian coastline that landed first on Bahrain, Ghateef and Yamama to then campaign along the northern Arabian coastline. The campaign in Bahrain was especially bitter, with Shapur II and the spah having to engage in close-quarter combat.173 After clearing the Arabs in Bahrain, Ghateef and Yamama, Shapur II struck deep into the Arabian hinterland, reaching all the way into Yathrib (later named Medina). The spah was overwhelmingly successful in defeating the Arabs, who at the height of their success had even occupied territory in Iran’s southwest. As a result of Shapur II’s military campaign, the Persian Gulf once again became safe for Sassanian maritime commerce, with Charax having been superseded by Astarabadh. Sassanian maritime ascendancy is affirmed by Ammianus Marcellinus who reported that ‘there are numerous towns and villages on every coast and frequent sailings of ships’. It is possible that the military port base at Siraf was built during Shapur II’s reign, in order to guard against future landings by Arab raiders.
By the time of Khosrow I Iranian naval technology had continued to advance, with notable innovations such as a redesigned rig and a system of five to seven sails. Sassanian vessels could now transport up to 700 passengers/troops and crew along with ‘a thousand metric tons of cargo’. The Sassanian navy is reported as having been capable of monitoring the security of Iranian maritime commerce in the Persian Gulf as well as protecting Iran’s southern Persian Gulf coastline against seaborne raids. Sassanian maritime capabilities were to prove vital in confronting a serious military threat during the reign of Khosrow I. The pro-Byzantine Abbysinian occupation of Arabia Felix (near modern Yemen) in 531 CE jeopardized Iranian hegemony in the Persian Gulf and even exposed Iran’s southern Persian Gulf coastline to naval attacks. The Sassanians could now be faced with a two-front war in which Byzantium could coordinate its land-based assaults into western and northwest Iran/Caucasus region with the naval landings of their Abbysinian allies along the southern Iranian coastline. Khosrow I responded by agreeing to support Yemenite anti-Abbysinian rebels led by Sayf Bin Dhu Yazan. A Sassanian fleet was launched from Iran’s southern ports to transport an expedition force led by Vahriz that landed near Aden. Khosrow I also had plans to secure the fortress of Petra along the Black Sea coast (in modern-day Georgia) to use as a Sassanian naval base on the Black Sea.
As noted by Sami, military ascendancy by the spah and the navy in the Persian Gulf had by the early 600s (1) allowed for a significant expansion in Sassanian maritime commerce far beyond the Persian Gulf; and (2) barred the Romans from dominating the Persian Gulf militarily, politically or economically. The Sassanians certainly displayed their naval capabilities during the long wars between Khosrow II and the Romano-Byzantines. As their armies reached the Mediterranean shores of modern-day Turkey, they built a fleet to attack the Aegean theatre. The Sassanian fleet attacked Constantia (Salamis) in 617 CE and then launched a naval attack against Rhodos (Rhodes) to capture this in 622 CE. The discovery of a hoard of Sassanian coins dated to 623 CE suggests that Samos may also have fallen to a Sassanian naval assault. Had Khosrow I been able to retain Petra and build a Black Sea fleet, the Romano-Byzantines would most likely have faced greater opposition to their naval landings in the Caucasus during Heraclius’ counteroffensives in 622–627 CE. The very long coastline of Armenia and northern Anatolia along the Black Sea allowed Heraclius to coordinate his naval landings in such a way as to allow him to outflank the Sassanian spah. When Heraclius launched his fleet from Constantinople towards the Black Sea’s Caucasian coastline there was no Sassanian navy in place to challenge this force. This allowed Heraclius to land his forces against no opposition in the region of modern day Circassia. Heraclius then linked up with the Khazars in 626 CE to attack the Sassanian region of Albania (modern-day Republic of Azerbaijan) in the Caucasus.
Towards the end of the Sassanian dynasty, however, the Arabs were to take advantage of Sassanian military weaknesses in the aftermath of the Khosrow II-Heraclius wars to invade Iran. Just as the Arabs were pushing into Sassanian Iran, Arab troops arrived by vessels to land along Iran’s southern Persian Gulf coastline to then push into the interior of the realm. The Arab ability to mount sea borne raids into Iran’s Persian Gulf coastline surfaced as late as the eighteenth and nineteenth century during the reigns of Iran’s Zand (1750–1794) and Qajar dynasties (1794–1925). Historically, Arab raids in the pre-Islamic and Islamic eras were made possible in those times when Iran lacked a navy and well-fortified ports an/d coastal bases.