Irawadi, or Irrawaddy, the principal river of Burma, long believed by many to have its origin in the Sanpo (q.v.), the great river of Tibet, which was shown in 1878-82 to be the upper waters of the Brahmaputra. In 25° 50' N. lat., a short distance above Bhamo, two arms, the Mali-kha and the Meh-kha, unite to form the river that is undoubtedly the Irawadi of Burma. From Bhamo the Irawadi winds 700 miles southward, throughout navigable for small boats, in spite of islands, sandbanks, and two rock-bound defiles. Its waters are muddy and its current generally rapid. Before reaching the sea, in nearly a dozen mouths, in the west of the Bay of Marta-ban, the river spreads out in a wide delta, 18,000 sq. m. in extent. Of its mouths two only are used by sea-going vessels, the Bassein on the west and the Rangoon on the east. The valley and plain of the Irawadi are very fertile, and grow vast quantities of rice. The river is the chief artery of the country : on its banks stand the principal towns, Bassein, Rangoon, Prome, Ava, Mandalay, Bhamo; its banks were the home of Burmese civilisation; its waters have served as the main means of communication not only to the interior of Burma, but to the south-western provinces of China and of Tibet. The river drains at least 158,000 sq. m. Its largest affluent, coming from the right hand, is the Chindwin. This and the two left-hand tributaries, the Shweli and Myit-nge, are alone navigable. The plain for 150 miles from the sea, being liable to inundations, has been protected by embankments since 1863.