Persian Gulf flooding of the basin started 15,000 years ago due to rising sea levels of the Holocene glacial retreat. This inland sea of some 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. In Iran this is called "Arvand Rood", where "Rood" means "river". Its length is , with Iran covering most of the northern coast and Saudi Arabia most of the southern coast. The Persian Gulf is about wide
Persian Gulf naming dispute the head of the Persian Gulf. This coincided with the early mapmaking efforts of Gerard Mercator, whose 1541 terrestrial globe attempts to give the most up-to-date information, naming the gulf "Sinus Persicus, nunc Mare de Balsera" ("Persian Gulf, now Sea of Basra"). However, on his world map of 1569, the name is changed to "Mare di Mesendin" (after the peninsula Ra's Musandam, in modern-day Oman), while his rival Abraham Ortelius, for the world atlas of 1570, opted for "Mare El Catif, olim Sinus Persicus" (after the Arabian port of Al Qatif), but labelled the entrance to the gulf the present-day