In 372 Firmus, a Mauretanian prince, rebelled against Roman rule and plunged the Diocese of Africa into disarray. Valentinian decided to give the command of the expedition to suppress the rebellion to Theodosius. The army was reorganized, extra troops were recruited, Theodosius' son was made "dux Moesiae Primae" replacing his father as commander in Illyricum and Theodosius himself started mustering his troops at Arles. In the spring of 373 Theodosius sailed to Africa and led a successful campaign against the rebels in the east of Mauritania. At the end of the campaigning season, when he led his army into western Mauritania, he suffered a major setback. In 374 Theodosius invaded western Mauritania again, this time he was more successful, defeating the rebels and capturing Firmus. In 373/374, the younger Theodosius was made "dux" of the province of Moesia Prima.