Details on the Mauretanian events of 39–44 are unclear. Cassius Dio wrote an entire chapter on the annexation of Mauretania by Caligula, but it is now lost. Caligula's move seemingly had a strictly personal political motive – fear and jealousy of his cousin Ptolemy – and thus the expansion may not have been prompted by pressing military or economic needs. However, the rebellion of Tacfarinas had shown how exposed Africa Proconsularis was to its west and how the Mauretanian client kings were unable to provide protection to the province, and it is thus possible that Caligula's expansion was a prudent response to potential future threats.