For thousands of years, most seawater pearls were retrieved by divers working in the Indian Ocean, in areas like the Persian Gulf, the Red Sea, and in the Gulf of Mannar. In the 14th-century Arabian Sea, the traveller Ibn Battuta provided the earliest known description of pearl diving by means of attaching a cord to the diver's waist. Before the beginning of the 20th century, pearl hunting was the most common way of harvesting pearls. Divers manually pulled oysters from ocean floors and river bottoms and checked them individually for pearls. Not all mussels and oysters produce pearls. In a haul of three tons, only three or four oysters may produce perfect pearls.