Trans-Saharan trade
On 25 July, Vogel left Tripoli with a caravan to catch up with Barth. Vogel arrived at the end of the Trans-Saharan trade route, Kuka, the capital of Bornu on 13 January 1854. Vogel's specimens, and the fact that both expedition engineers were soldiers, made the king there suspicious of his intentions, and Vogel's movements were severely restricted.