Mauretania was a client kingdom of Rome ruled by Ptolemy of Mauretania . Caligula invited Ptolemy to Rome and then suddenly had him executed.  Mauretania was annexed by Caligula and subsequently divided into two provinces, Mauretania Tingitana and Mauretania Caesariensis , separated by the river Malua .  Pliny claims that division was the work of Caligula, but Dio states that in AD 42 an uprising took place, which was subdued by Gaius Suetonius Paulinus and Gnaeus Hosidius Geta, and the division only took place after this.  This confusion might mean that Caligula decided to divide the province, but the division was postponed because of the rebellion.  The first known equestrian governor of the two provinces was Marcus Fadius Celer Flavianus, in office in AD 44.