The classic Chinese sailing vessel of ancient unknown origin, still in wide use. High-sterned, with projecting bow, the junk carries up to five masts on which are set square sails of panels of linen or matting flattened by bamboo strips. Each sail can be spread or closed at a pull, like a venetian blind. The massive rudder takes the place of a keel, or centreboard. The hull is partitioned by solid bulkheads running both transversely and longitudinally, adding greatly to strength. Chinese junks sailed to Indonesian and Indian waters by the early Middle Ages. Junks were used as seagoing vessels as early as the 2nd century AD and developed rapidly during the Song dynasty (960–1279). They evolved in the later dynasties, and were used throughout Asia for extensive ocean voyages. They were found, and in lesser numbers are still found, throughout South-East Asia and India, but primarily in China. Found more broadly today is a growing number of modern recreational junk-rigged sailboats.