During the time of Augustus, there were initially two treasuries until 6 AD when a third one was created. Extensive changes were made to the operations of state finances during the time of Augustus, but the picture is often not clear, especially in the details. What follows is a summary of (sometimes conflicting) academic sources.
Aerarium Saturni (sometimes referred to as the Senatorial Treasury). This was the main state treasury of Rome and was based at the Temple of Saturn, below the Capitol. Under Augustus, it was administered by two praetors (magistrates). Financial records were kept at the nearby Tabularium.
Fiscus (originally meaning ‘money-bag’ or ‘basket’) or Privy-Purse. This is also referred to as the Imperial Treasury in some sources but was not, strictly speaking, a treasury in the the time of Augustus. Rather, it denoted the private funds of Augustus (and subsequent emperors) as well as the financial administration controlled by him. The emperor’s Fiscus was not formally established until the reign of Nero. The term ‘Fiscus’ was also used to refer the funds of provincial governors, though at what point these formally became treasuries is unclear.
- Aerarium Militare (Military Treasury). Located on the Capitol, this was established by Augustus in 6 AD. Three senators, effectively dependent upon Augustus, served as prefects of the military fund.
The sources of the funds of these three financial ‘bodies’ is either not entirely clear and / or varied at different times.
Funds for the Aerarium Saturni came from taxes, tributes, customs and various other sources. It certainly included revenue from senatorial provinces and was supposed to have included revenue from imperial provinces. Werner Eck, in The Age of Augustus, says
...the state treasury (aerarium Saturni), into which all state income,
including taxes from Augustus’ own provinces, was declared to flow for
legal and accounting purposes.
However, The Cambridge Companion to the Roman Economy states
...imperial estates in North Africa and public lands in Egypt. All of
these lands formed part of a widespread network of properties under
the control of the imperial treasury, or fiscus..
This would appear to directly contradict Eck, but we should probably interpret it thus: Eck is saying what should have happened (and maybe did at times) while the Cambridge Companion is saying what actually did happen (at least usually).
For the Fiscus, Augustus inherited a vast fortune and this was the foundation of his wealth, but he also ‘diverted’ unknown amounts from imperial provinces into his own accounts, money which should (technically at least) have gone to the Aerarium Saturni.
As Augustus would also sometimes transfer amounts to Aerarium Saturni from his personal fortune when funds ran low, Anthony Everitt’s overall assessment, in Augustus: The Life of Rome’s First Emperor, seems appropriate:
In practice, it was difficult to distinguish between the treasury and
the privy purse.
The Aerarium Militare was given a ‘starting’ fund of 170,000,000 sesterces from Augustus’ Fiscus. Otherwise, it was financed by two new taxes: an inheritance and large bequests tax of 5% (vicesima hereditatium) and a sales tax of 1%. There were also donations from cities and client kings.
The Aerarium Saturni was supposed to cover all state expenses: roads, salaries for the legions, military pensions (up to 6 AD), public buildings etc, and even those of the emperor, but Augustus had to step in at times, either transferring money or meeting certain expenses himself. In 20 BC, for example, he effectively took over responsibility for roads (the cura viarum) by transferring money to the Aerarium Saturni. He also paid soldiers pensions out of his personal fortune as the Aerarium Saturni did not have sufficient funds. When the Aerarium Militare was set up in 6 AD, it took over soldiers’ pensions. It appears that Augustus also covered most, if not all, expenses, in the imperial provinces.
As Augustus left considerably less in his will (150,000,000 sesterces) than he had inherited (1,400,000,000 sesterces) we can surmize that, although he apparently diverted income from imperial provinces into the fiscus, these amounts were greatly exceeded by the expenses he covered for the Aerarium Saturni – the military pensions alone were a huge drain on his resources.
David Shotter, in Augustus Caesar, summarizes their role as
not so much a deposit of cash as a statement of income and outgoings
relating to each province; these accounts were supplemented, where
necessary, with grants from the aerarium.
Thus, as Anthony Everitt states,
...it is unlikely that large sums of money moved to and from Rome.
Each province had its own treasury, from which the princeps would draw
for local military and administrative purposes, and in many cases
there would not have been a large surplus to send to Rome.
Pat Southern – Augustus
Pat Southern – The Roman Army
G.W. Bowersock - Augustus and the Greek World
Suetonius - The Life of Augustus
John Buchan - Augustus