The name "Colombo", first introduced by the Portuguese in 1505, is believed to be derived from the classical Sinhalese name කොළොම්තොට Kolon thota, meaning “port on the river Kelani"
Another belief is that the name is derived from the Sinhalese name කොල-අඹ-තොට Kola-amba-thota which means "Harbour with leafy mango trees". This coincides with Robert Knox's history of the island while he was a prisoner in Kandy. He writes that, "On the West the City of Columbo, so called from a Tree the Natives call Ambo, (which bears the Mango-fruit) growing in that place; but this never bare fruit, but onely leaves, which in their Language is Cola and hence they called the Tree Colambo: which the Christians in honour of Columbus turned to Columbo.
The author of the oldest Sinhalese grammar, Sidatsangarava, written in the 13th century wrote about a category of words that exclusively belonged to early Sinhalese. It lists naramba (to see) and kolamba (for or harbour) as belonging to an indigenous source. Kolamba may also be the source of the name of the commercial capital Colomb
As Colombo possesses a natural harbour, it was known to Indian, Greek, Persian, Roman, Arab, and Chinese traders over 2,000 years ago. Traveller Ibn Battuta who visited the island in the 14th century, referred to it as Kalanpu. Arabs, whose prime interests were trade, began to settle in Colombo around the 8th century AD mostly because the port helped their business by the way of controlling much of the trade between the Sinhalese kingdoms and the outside world. Their descendants now comprise the local Sri Lankan Moor community.