The Gulf of Morbihan is a natural harbour on the coast of the department of Morbihan in southern Brittany, France. Its English name is taken from the French version, le golfe du Morbihan, though it would be more precisely called 'the Morbihan' as its Breton name 'Ar Mor Bihan means 'the little sea'. (Compare the Welsh y môr bychan), as opposed to the Atlantic Ocean outside, (Ar Mor Bras) Legend says that there are as many islands in the Gulf as there are days of the year. In fact the gulf has about 40, depending on the tides. Many islands are private property, except the largest two, Île-aux-Moines and Île-d'Arz.
The area around the gulf features an extraordinary range of megalithic monuments. There are passage dolmens, stepped pyramids with underground dolmen chambers, stone circles, and giant menhirs, among others. The site best known to outsiders is Carnac, where remains of a dozen rows of huge standing stones run for over ten kilometers. The passage grave of Gavrinis, on a small island in the Gulf, is one of the most important such sites in Europe. Some of the ruins have been dated to at least 3300 BC — 200 years older than England's Stonehenge.