If I remember correctly, only non-citizens were taxed, but what kind of taxes were there? Were there other ways to make money off of residents, like a business profit tax or something similar? Was there a deficit that had to be filled via some other source?
This thread talks about the tax system, particularly that of the early Principate and later Republic. Systems of tax collection and their rates were highly variable, not only across the centuries that the Roman state maintained provincial holdings but even from province to province. Further, the difference between taxation, tribute, and other revenue collected was not always obviously drawn, especially in the late Republic