While there are over thirty islands in the bay, the three largest are Aquidneck Island, Conanicut Island, and Prudence Island. Bodies of water that are part of Narragansett Bay include the Sakonnet River; Mount Hope Bay; and the southern, tidal part of the Taunton River. The bay opens on Block Island Sound — Block Island lies less than 20 miles southwest of its opening — and the Atlantic Ocean. Bridges over parts of the bay include two suspension bridges, the Claiborne Pell Newport Bridge and Mount Hope Bridge, the Jamestown-Verrazano Bridge, and the Braga Bridge which forms the Narragansett Bay crossing of United States Interstate 195.
As the ice stalled, then retreated, the region became ice-free by about 14,000 B.P. A complicated sequence of marine ingression and isostatic rebound flooded and emptied the landscape. A fresh water proglacial lake called by geologists Lake Narragansett formed about 15,500 B.P., impounded behind terminal moraines: the lake lasted about 500 years, leaving the powerful flow of a post-glacial river running down its north-south axis. Then salt water filled the valley, as rising sea levels permanently flooded the area.
It is accepted by most historians that first contact by Europeans was made by Giovanni da Verrazzano, an Italian explorer who entered the bay in his ship La Dauphine in 1524 after visiting New York Bay. Verrazzano called the bay Refugio, the "Refuge". The bay has several entrances, however, and the exact route of his voyage and the location where he laid anchor is still a subject of dispute among historians, leading to a corresponding uncertainty over which tribe made contact with him. Verrazzano reported that he found clearings and open forests suitable for travel "even by a large army," a far cry from the impenetrable tangle that resulted when the English suppressed controlled burns in the seventeenth century.
The first recorded European settlement was in the 1630s. Roger Williams, a dissatisfied member of the Plymouth Colony, moved into the area around the year 1636. He made contact with the Narragansett sachem called Canonicus by the Europeans, and set up a trading post on the site of Providence. At the same time, the Dutch had established a trading post approximately 12 miles to the southwest which was under the authority of New Amsterdam in New York Bay.
In 1643, Williams traveled to England and was granted a charter for the new colony of Rhode Island. He also wrote a dictionary of the Narragansett language, Keys to the Indian Language, which was published in England that same year.
The Gaspée Affair, an important naval event of the American Revolution, occurred in 1772 in the bay; it involved the capture of the HMS Gaspee, a British ship. The American victory contributed to the eventual start of the war at the Battles of Lexington and Concord in Massachusetts 3 years later. The event is celebrated in Warwick as the Gaspee Days Celebration in June, which event includes a symbolic recreation of the burning of the ship.
Roger Williams and other early colonists named many of the islands in the bay. To remember the names, colonial school children often recited the poem: "Patience, Prudence, Hope and Despair. And the little Hog over there.