Persian Gulf

Shallow, hot, and saltier than the open ocean, the Persian Gulf is a modest body of water that carries an outsized weight in world affairs. Cupped between Iran and the Arabian Peninsula, it sits atop the richest concentration of oil and gas on the planet, and the tankers that thread its single narrow exit at the Strait of Hormuz carry a fifth of the world's traded petroleum. For millennia it has also been a sea of pearls, dhows, and ancient trade between Mesopotamia, Arabia, and India.

Covering only about 251,000 square kilometres and averaging around 50 metres deep, the Gulf is one of the shallowest seas of its size, reaching just 90 metres at its deepest. Fierce evaporation under the desert sun and little river inflow — chiefly the combined Tigris and Euphrates at the marshy Shatt al-Arab — make its waters intensely saline and among the warmest on Earth, with summer surface temperatures that stress its corals. Its only link to the wider ocean is the Strait of Hormuz, opening into the Gulf of Oman and the Arabian Sea.

The Gulf cradled some of humanity's earliest cities along the rivers that feed it, and its pearl banks sustained the region's economy until the twentieth century. The discovery of oil transformed sleepy ports into the gleaming cities of Kuwait, Doha, Abu Dhabi, and Dubai, and made the waterway a permanent focus of global strategy and conflict. Eight nations share its coast, and the security of Hormuz remains one of the most closely watched questions in international politics.

• Arabian Sea
  The monsoon-driven sea linking Arabia, Africa, and India connects to
• Indian Ocean
  The world's third-largest and warmest ocean drains to
• Euphrates
  The longer river of Mesopotamia, cradle of cities feeds from
• Tigris
  The swifter river of Mesopotamia, past Baghdad and Mosul feeds from
• Asia
  Earth's largest and most populous continent located on