This inland sea of some 251,000 square kilometres (96,912 sq mi) is connected to the Gulf of Oman in the east by the Strait of Hormuz; and its western end is marked by the major river delta of the Shatt al-Arab, which carries the waters of the Euphrates and the Tigris. Its length is 989 kilometres (615 miles), with Iran covering most of the northern coast and Saudi Arabia most of the southern coast. The Persian Gulf is about 56 km (35 mi) wide at its narrowest, in the Strait of Hormuz. The waters are overall very shallow, with a maximum depth of 90 metres (295 feet) and an average depth of 50 metres (164 feet).
Countries with a coastline on the Persian Gulf are (clockwise, from the north): Iran; Oman's exclave Musandam; the United Arab Emirates; Saudi Arabia; Qatar, on a peninsula off the Saudi coast; Bahrain, on an island; Kuwait; and Iraq in the northwest. Various small islands also lie within the Persian Gulf, some of which are the subject of territorial disputes between the states of the region.
The International Hydrographic Organization defines the Persian Gulf's southern limit as "The Northwestern limit of Gulf of Oman". This limit is defined as "A line joining Ràs Limah (25°57'N) on the coast of Arabia and Ràs al Kuh (25°48'N) on the coast of Iran (Persia)".
The Persian Gulf and its coastal areas are the world's largest single source of crude oil, and related industries dominate the region. Safaniya Oil Field, the world's largest offshore oilfield, is located in the Persian Gulf. Large gas finds have also been made, with Qatar and Iran sharing a giant field across the territorial median line (North Field in the Qatari sector; South Pars Field in the Iranian sector). Using this gas, Qatar has built up a substantial liquefied natural gas (LNG) and petrochemical industry.
In 2002, the Persian Gulf nations of Bahrain, Iran, Iraq, Kuwait, Qatar, Saudi Arabia, and the UAE produced about 25% of the world's oil, held nearly two-thirds of the world's crude oil reserves, and about 35% of the world's natural gas reserves. The oil-rich countries (excluding Iraq) that have a coastline on the Persian Gulf are referred to as the Persian Gulf States. Iraq's egress to the gulf is narrow and easily blockaded consisting of the marshy river delta of the Shatt al-Arab, which carries the waters of the Euphrates and the Tigris rivers, where the east bank is held by Iran.
In 550 BC, the Achaemenid Empire established the first ancient empire in Persis (Pars, or modern Fars), in the southwestern region of the Iranian plateau. Consequently, in the Greek sources, the body of water that bordered this province came to be known as the "Persian Gulf".
During the years 550 to 330 BC, coinciding with the sovereignty of the Achaemenid Persian Empire over the Middle East area, especially the whole part of the Persian Gulf and some parts of the Arabian Peninsula, the name of "Pars Sea" is widely found in the compiled written texts.
In the travel account of Pythagoras, several chapters are related to description of his travels accompanied by the Achaemenid king Darius the Great, to Susa and Persepolis, and the area is described. From among the writings of others in the same period, there is the inscription and engraving of Darius the Great, installed at junction of waters of Red Sea and the Nile river and the Rome river (current Mediterranean) which belongs to the 5th century BC where Darius the Great has named the Persian Gulf Water Channel: "Pars Sea" ("Persian Sea").
Considering the historical background of the name Persian Gulf, Sir Arnold Wilson mentions in a book published in 1928 that "no water channel has been so significant as Persian Gulf to the geologists, archaeologists, geographers, merchants, politicians, excursionists, and scholars whether in past or in present. This water channel which separates the Iran Plateau from the Arabia Plate, has enjoyed an Iranian Identity since at least 2200 years ago."
Before being given its present name, the Persian Gulf was called many different names. The classical Greek writers, like Herodotus, called it "the Red Sea". In Babylonian texts, it was known as "the sea above Akkad".
The name of the gulf, historically and internationally known as the Persian Gulf after the land of Persia (Iran), has been disputed by some Arab countries since the 1960s. Rivalry between Iran and some Arab states, along with the emergence of pan-Arabism and Arab nationalism, has seen the name Arabian Gulf become predominant in most Arab countries. Names beyond these two have also been applied to or proposed for this body of water.
The world's oldest known civilization (Sumer) developed along the Persian Gulf and southern Mesopotamia. The shallow basin that now underlies the Gulf was an extensive region of river valley and wetlands during the transition between the end of the Last Glacial Maximum and the start of the Holocene, which, according to University of Birmingham archaeologist Jeffrey Rose, served as an environmental refuge for early humans during periodic hyperarid climate oscillations, laying the foundations for the legend of Dilmun.
For most of the early history of the settlements in the Persian Gulf, the southern shores were ruled by a series of nomadic tribes. During the end of the fourth millennium BC, the southern part of the Persian Gulf was dominated by the Dilmun civilization. For a long time the most important settlement on the southern coast of the Persian Gulf was Gerrha. In the 2nd century the Lakhum tribe, who lived in what is now Yemen, migrated north and founded the Lakhmid Kingdom along the southern coast. Occasional ancient battles took place along the Persian Gulf coastlines, between the Sassanid Persian empire and the Lakhmid Kingdom, the most prominent of which was the invasion led by Shapur II against the Lakhmids, leading to Lakhmids' defeat, and advancement into Arabia, along the southern shore lines. During the 7th century the Sassanid Persian empire conquered the whole of the Persian Gulf, including southern and northern shores.
Between 625 BC and 226 AD, the northern side was dominated by a succession of Persian empires including the Median, Achaemenid, Seleucid and Parthian empires. Under the leadership of the Achaemenid king Darius the Great (Darius I), Persian ships found their way to the Persian Gulf. Persian naval forces laid the foundation for a strong Persian maritime presence in Persian Gulf, that started with Darius I and existed until the arrival of the British East India Company, and the Royal Navy by mid-19th century AD. Persians were not only stationed on islands of the Persian Gulf, but also had ships often of 100 to 200 capacity patrolling empire's various rivers including Shatt-al-Arab, Tigris, and the Nile in the west, as well as Sind waterway, in India.
The Achaemenid high naval command had established major naval bases located along Shatt al-Arab river, Bahrain, Oman, and Yemen. The Persian fleet would soon not only be used for peacekeeping purposes along the Shatt al-Arab but would also open the door to trade with India via Persian Gulf.
Following the fall of Achaemenid Empire, and after the fall of the Parthian Empire, the Sassanid empire ruled the northern half and at times the southern half of the Persian Gulf. The Persian Gulf, along with the Silk Road, were important trade routes in the Sassanid empire. Many of the trading ports of the Persian empires were located in or around Persian Gulf. Siraf, an ancient Sassanid port that was located on the northern shore of the gulf, located in what is now the Iranian province of Bushehr, is an example of such commercial port. Siraf, was also significant in that it had a flourishing commercial trade with China by the 4th century, having first established connection with the far east in 185 AD.
Portuguese expansion into the Indian Ocean in the early 16th century following Vasco da Gama's voyages of exploration saw them battle the Ottomans up the coast of the Persian Gulf. In 1521, a Portuguese force led by commander Antonio Correia invaded Bahrain to take control of the wealth created by its pearl industry. On April 29, 1602, Shāh Abbās, the Persian emperor of the Safavid Persian Empire expelled the Portuguese from Bahrain, and that date is commemorated as National Persian Gulf day in Iran. With the support of the British fleet, in 1622 'Abbās took the island of Hormuz from the Portuguese; much of the trade was diverted to the town of Bandar 'Abbās, which he had taken from the Portuguese in 1615 and had named after himself. The Persian Gulf was therefore opened by Persians to a flourishing commerce with the Portuguese, Dutch, French, Spanish and the British merchants, who were granted particular privileges. The Ottoman Empire reasserted itself into Eastern Arabia in 1871. Under military and political pressure from the governor of the Ottoman Vilayet of Baghdad, Midhat Pasha, the ruling Al Thani tribe submitted peacefully to Ottoman rule. The Ottomans were forced to withdraw from the area with the start of World War I and the need for troops in various other frontiers.
In World War II, the Western Allies used Iran as a conduit to transport military and industrial supply to the USSR, through a pathway known historically as the "Persian Corridor". Britain utilized the Persian Gulf as the entry point for the supply chain in order to make use of the Trans-Iranian Railway. The Persian Gulf therefore became a critical maritime path through which the Allies transported equipment to Russia against the Nazi invasion.
From 1763 until 1971, the British Empire maintained varying degrees of political control over some of the Persian Gulf states, including the United Arab Emirates (originally called the Trucial States) and at various times Bahrain, Kuwait, Oman, and Qatar through the British Residency of the Persian Gulf.
The United Kingdom maintains a high profile in the region to date; in 2006 alone, over 1 million British nationals visited Dubai. In 2014, the UK announced it will reestablish a permanent military base, HMS Jufair, in the Persian Gulf, the first since it withdrew from East of Suez in 1971.
The Persian Gulf is home to many small islands. Bahrain, an island in the Persian Gulf, is itself a Persian Gulf Arab state. Geographically the biggest island in the Persian Gulf is Qeshm island located in the Strait of Hormuz and belonging to Iran. Other significant islands in the Persian Gulf include Greater Tunb, Lesser Tunb and Kish administered by Iran, Bubiyan administered by Kuwait, Tarout administered by Saudi Arabia, and Dalma administered by UAE. In recent years, there has also been addition of artificial islands, often created by Arab states such as UAE for commercial reasons or as tourist resorts. Although very small, these artificial islands have had a negative impact on the mangrove habitats upon which they are built, often causing unpredictable environmental issues. Persian Gulf islands are often also historically significant, having been used in the past by colonial powers such as the Portuguese and the British in their trade or as acquisitions for their empires.
Eight nations have coasts along the Persian Gulf: Bahrain, Iran, Iraq, Kuwait, Oman, Qatar, Saudi Arabia, and the United Arab Emirates. The gulf's strategic location has made it an ideal place for human development over time. Today, many major cities of the Middle East are located in this region.
The wildlife of the Persian Gulf is diverse, and entirely unique due to the gulf's geographic distribution and its isolation from the international waters only breached by the narrow Strait of Hormuz. The Persian Gulf has hosted some of the most magnificent marine fauna and flora, some of which are near extinction or at serious environmental risk. From corals, to dugongs, Persian Gulf is a diverse cradle for many species who depend on each other for survival.
A great example of this symbiosis are the mangroves in the gulf, which require tidal flow and a combination of fresh and salt water for growth, and act as nurseries for many crabs, small fish, and insects; these fish and insects are the source of food for many of the marine birds that feed on them. Mangroves are a diverse group of shrubs and trees belonging to the genus Avicennia or Rhizophora that flourish in the salt water shallows of the gulf, and are the most important habitats for small crustaceans that dwell in them. They are as crucial an indicator of biological health on the surface of the water, as the corals are to biological health of the gulf in deeper waters. Mangroves' ability to survive the salt water through intricate molecular mechanisms, their unique reproductive cycle, and their ability to grow in the most oxygen-deprived waters have allowed them extensive growth in hostile areas of the gulf. Unfortunately, however, with the advent of artificial island development, most of their habitat is destroyed, or occupied by man-made structures. This has had a negative impact on the crustaceans that rely on the mangrove, and in turn on the species that feed on them.
Along the mediterranean regions of the Arabian Sea, including the Persian Gulf, the Red Sea, the Gulf of Kutch, the Gulf of Suez, the Gulf of Aqaba, the Gulf of Aden, and the Gulf of Oman, dolphins and finless porpoises are the most common marine mammals in the waters, while larger whales and orcas are rarer today. Historically, whales had been abundant in the gulf before commercial hunts wiped them out. Whales were reduced even further by illegal mass hunts by the Soviet Union and Japan in the 1960s and 70s. Alongside Bryde's whales, the most common and possible resident and still can be seen in deeper marginal seas such as Gulf of Aden, Israel coasts, and in Strait of Hormuz. Other species such as the critically endangered Arabian humpback whale (historically common in Gulf of Aden, and sighting records increased in Red Sea since in 2006 including in Gulf of Aqaba), omura's whale, minke whale, and orca also swim into the gulf, while many other large species such as blue whale, sei, and sperm whales were once migrants into the Gulf of Oman and off the coasts in deeper waters, and still migrate in Red Sea, but mainly in deeper waters of outer seas.
One of the more unusual marine mammals living in the Persian Gulf is the Dugong dugon, commonly referred to as the dugong. Called "sea cows" for their grazing habits, their mild manner and resemblance to the livestock, dugongs have a life expectancy similar to that of humans and can reach lengths of up to 3 metres (9.8 feet). These gentle mammals feed on the sea grass and genetically resemble the land mammals more than the dolphins and the whales. Despite the simplicity of their grass diet, new developments along the Persian Gulf coastline, particularly artificial island development in Arab states, pollution particularly by oil spills caused during the "Persian Gulf war" and also due to occasional oil spills, and uncontrolled hunting has had a negative impact on the survival of the dugongs. After Australian waters with some 80,000 dugong inhabitants, the waters off Qatar, Bahrain, UAE, and Saudi Arabia have some 7,500 dugongs remaining, making the Persian Gulf the second most important habitat for the species. Dugong's current number is dwindling and it is not clear how many are currently alive or what their reproductive trend is. Unfortunately, ambitious and uncalculated construction schemes, political unrest and an ever-present international conflict, and presence of the most lucrative world supply of oil, along with lack of cooperation between Arab states and Iran, has had a negative impact on the survival of many marine species, including dugongs.
The Persian Gulf is also home to many migratory and local birds. There is great variation in color, size, and type of the bird species that call the gulf home. One bird in particular, the kalbaensis, a sub-species of the kingfishers is at the brink of extinction due to real state development by cities such as Dubai and countries such as Oman. Estimates from 2006 showed that only three viable nesting sites were available for this ancient bird, one located 80 miles (129 km) from Dubai, and two smaller sites in Oman, all of which are in the process of becoming real estate developments. Such expansion would prove devastating and could cause this species to become extinct. Unfortunately for the kingfisher, a U.N. plan to protect the mangroves as a biological reserve was blatantly ignored by the emirate of Sharjah, which allowed the dredging of a channel that bisects the wetland and construction of an adjacent concrete walkway. Environmental watchdogs in Arabia are few, and those that do advocate the wildlife are often silenced or ignored by developers of real estate, most of whom have royal family connections and huge energy profits to invest. The end result has been sacrifice of a beautiful yet delicate ecology that has been in harmony for hundreds of years, for structures that are erected only a few years, yet will have a lasting detrimental effect.
Almost no species in the Persian Gulf is spared from the real estate development of UAE and Oman, including the hawksbill turtle, the flamingo, and the booted warblers, mainly due to destruction of the mangrove habitats to make way for towers, hotels, and luxury resorts. Even dolphins that frequent the gulf in northern waters, around Iran are at serious risk. Recent statistics and observations show that dolphins are at danger of entrapment in purse seine fishing nets and exposure to chemical pollutants; perhaps the most alarming sign is the "mass suicides" committed by dolphins off Iran's Hormozgan province, which are not well understood, but are suspected to be linked with a deteriorating marine environment from water pollution from oil, sewage, and industrial run offs.
The Persian Gulf is also home to over 700 species of fish, most of which are native to the gulf. Of these 700 species, more than 80% are coral reef associated, and directly or indirectly depend on the coral reef for their survival. Overall, the wild life of the Persian Gulf is endangered from both global factors, and regional, local negligence. Most pollution is from ships; land generated pollution counts as the second most common source of pollution, ranging from mercury, to acidic or basic toxins.
Coral is another important inhabitant of the Persian Gulf waters. Corals are vital ecosystems that support multitude of marine species, and whose health directly reflects the health of the gulf. Recent years have seen a drastic decline in the coral population in the gulf, partially owing to global warming but majorly due to irresponsible dumping by Arab states like the UAE and Bahrain. Construction garbage such as tires, cement, and chemical by products have found their way to the Persian Gulf in recent years. Aside from direct damage to the coral, the construction waste creates "traps" for marine life in which they are trapped and die. The end result has been a dwindling population of the coral, and as a result a decrease in number of species that rely on the corals for their survival.