The rationalis was the Roman Empire's chief financial minister prior to the reforms of Emperor Diocletian and the Late Empire. Among the tasks of the rationalis were the collection of all normal taxes payable in coin and duties, the control of the currency, and the administration of mines, mints, imperial arsenals and worked closely with the magister rei privatae (manager of imperial estates and city properties) until about 350, when the res privata gained autonomy. After the reforms of Diocletian and Constantine the Great, the rationalis was succeeded by the comes sacrarum largitionum, but the rationales continued to exist in the provinces (e.g. the comes et rationalis summarum Aegypti), as supervisors of the public treasury and the emperor's private domains (res privata). In the 6th century, the post was increasingly rendered into its Greek equivalent, logothetes, which later was given to the senior fiscal secretaries of the middle Byzantine Empire (7th–12th centuries).