A rationibus 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 secretary of finance, in charge of maintaining the accounts and expenditures of the fiscus

Fiscus

Fiscus, from which comes the English term fiscal, was the name of the personal treasury of the emperors of Rome. The word is literally translated as "basket" or "purse" and was used to describe those forms of revenue collected from the provinces , which were then granted to the emperor...

 which is the imperial treasury. This official's role in the finances

Roman finance

For centuries the monetary affairs of the Roman Republic had rested in the hands of the Senate. These elite liked to present themselves as steady and fiscally conservative, but as the 19th-century historian of Rome Wilhelm Ihne remarked:...

 of the Early Empire was considerable. The office was originally held by a freedman, but from the 2nd century AD and the reign of Hadrian

Hadrian

Hadrian , was Roman Emperor from 117 to 138. He is best known for building Hadrian's Wall, which marked the northern limit of Roman Britain. In Rome, he re-built the Pantheon and constructed the Temple of Venus and Roma. In addition to being emperor, Hadrian was a humanist and was philhellene in...

, Equestrians (Equites) assumed total control after the reputation of freedman declined due to corruption. The rationibus was rendered unnecessary by the comes sacrarum largitionum (master of the sacred largess) of the 4th century AD.