The rationalis was the Roman Empire

Roman Empire

The Roman Empire was the post-Republican period of the ancient Roman civilization, characterised by an autocratic form of government and large territorial holdings in Europe and around the Mediterranean....

's chief financial minister prior to the reforms of Emperor Diocletian

Diocletian

Diocletian |latinized]] upon his accession to Diocletian . c. 22 December 244  – 3 December 311), was a Roman Emperor from 284 to 305....

 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 privatae gained autonomy. After the reforms of Diocletian

Diocletian

Diocletian |latinized]] upon his accession to Diocletian . c. 22 December 244  – 3 December 311), was a Roman Emperor from 284 to 305....

 and Constantine the Great, the rationalis was succeeded by the comes sacrarum largitionum

Comes sacrarum largitionum

The comes sacrarum largitionum was one of the senior fiscal officials of the late Roman Empire and the early Byzantine Empire....

. As a comes

Comes

Comes , plural comites , is the Latin word for companion, either individually or as a member of a collective known as comitatus, especially the suite of a magnate, in some cases large and/or formal enough to have a specific name, such as a cohors amicorum. The word comes derives from com- "with" +...

("count"), he was a member of the imperial consistory.