taxation is was a bit
more complex than a monetary value.
Remember it wasn't until very late on in the Empire that there was even a monetary economy in rural areas. My main reference has been coin loss patterns in Roman Britain
but I would assume a similar situation would be found throughout the Empire, given that it wasn't until the time of Diocletian
that every province has a central mint and therefore a local, regular coin supply.
period is interesting as there was very little taxation, as all public service was unpaid. This included civil and military
service. Therefore taxes were only really levied in emergencies in the form of a personal tax called the "tributum". This was calculated as a percentage of ones wealth and was usually employed to pay for wars. It was not technically a tax though more of a loan as should there be spoils from the war the "tributum" would be returned.
With the conquest of Italy
cam further sources of revenue and the "tributum" fell out of use by 167BC. Tax then came in from four different avenues...
1) "Ager Publicus" - This was public land, which tenants paid a portion of their income (usually as material products not in coin) as rent.
Tributes - This was a fixed sum expected as tribute from each province. It was usually paid every five years and was collected by the local government in any way they see fit (Verres' rather cruel methods are described in Cicero
"Against Verres"), although in some provinces it was generally a tithe (10%) of their produce. The companies in charge of collectin were contractors called "mancipes" and the actual revenue collectors themselves went by the name of "publicani"
3) Individual Taxes - Some regions had
specific taxes for certain acts. eg. Port
tax (duty on incoming ships
), Frontier Tax (duty on frontier imports) and various other tolls (road toll, market tolls etc)
You can find out about these in various legal codexes but one example could be the "Lex Manlia
", which was a 5% tax on the value of a manumitted slave levied from 357BC.
4) General state monopolies - While this was not a "tax" as such it still ensured the stae offers were filled. The state ran
the fisheries and the mines and therefore ensured all profits from this went directly to them.
I know this hardly answers your question but it's all I know about Roman
taxation and state finances. If I get the chance I will dig out some sources for you.