The Indus River (: Darya-e Sindh, ) is one of the longest rivers in Asia. It flows through Pakistan, Jammu and Kashmir and western Tibet. Originating in the Tibetan Plateau in the vicinity of Lake Mansarovar, the river runs a course through the Ladakh region of Jammu and Kashmir, towards Gilgit-Baltistan and then flows in a southerly direction along the entire length of Pakistan to merge into the Arabian Sea near the port city of Karachi in Sindh. The total length of the river is . It is Pakistan’s longest river. The river has a total drainage area exceeding . Its estimated annual flow stands at around , making it the twenty-first largest river in the world in terms of annual flow. The Zanskar is its left bank tributary in Ladakh. In the plains, its left bank tributary is the Chenab which itself has four major tributaries, namely, the Jhelum, the Ravi, the Beas and the Sutlej. Its principal right bank tributaries are the Shyok, the Gilgit, the Kabul, the Gomal and the Kurram. Beginning in a mountain spring and fed with glaciers and rivers in the Himalayas, the river supports ecosystems of temperate forests, plains and arid countryside. The Indus forms the delta of present-day Pakistan mentioned in the Vedic Rigveda as Sapta Sindhu and the Iranian Zend Avesta as Hapta Hindu (both terms meaning “seven rivers”). The river has been a source of wonder since the Classical Period, with King Darius of Persia sending his Greek subject Scylax of Caryanda to explore the river as early as 510 BC.