Why it's the capital
Arab traders settled around its port from about the 8th century, and later the Portuguese and then the Dutch took control. When the whole island passed to the British in 1815, Colombo became its capital.
Capital of Sri LankaFacing the Indian Ocean on the west coast of Sri Lanka, Colombo has the mouth of the Kelani River at its northern edge.
Arab traders settled around its port from about the 8th century, and later the Portuguese and then the Dutch took control. When the whole island passed to the British in 1815, Colombo became its capital.
Picture Sri Lanka as a teardrop below the tip of India: Colombo is on its west coast, in the southern half of the island.
In the 1980s the parliament moved to Sri Jayawardenepura Kotte, right next to Colombo, and Kotte became the official capital. Colombo is still the executive and judicial capital and the largest city.
Sources: Wikipedia: Colombo