A rationalis was a high-ranking fiscal officer in the Roman Empire.
[1] Until replaced by the comes sacrarum largitionum by Emperor Constantine in the early 4th century, the rationalis summarum – comparable to a modern-day finance minister – was one of two state officials who had authority over the imperial treasury, the other one being the rationalis rei privatae (manager of imperial estates and city properties).
[1][2] Examples for tasks that were performed by a rationalis are "the collection of all normal taxes and duties, the control of currency and the administration of mines and mints".
[1] Each province also had various classes of rationales,[3] and Emperor Diocletian's administrative reforms had mirrored the dual structure on the diocesis–level, instituting the local positions rationalis summarum and magister rei privatae above the procuratores.
[2] The former continued to exist after the reforms, one example are the comes et rationalis summarum Aegypti.