While in Sierra Leone he also collected linguistic material from many African languages, some of it from freed slaves such as Ali Eisami, a Kanuri man. Koelle's major work, Polyglotta Africana (1854), is considered the beginning of the serious study of a large range of African languages by European scholars.
During his time in Sierra Leone, he collected linguistic data from various African languages, including some gathered from freed slaves like Ali Eisami, a Kanuri man. Koelle's significant work, Polyglotta Africana (1854), is considered the starting point for serious European research on a broad spectrum of African languages.