What was the Roman 1% tax on auctions and sales called?

The Roman 1% tax on auctions and sales was called the centesima rerum venalium.

Its Latin name means roughly “one-hundredth of things sold,” describing its original rate of one percent. The tax was associated with public auctions and commercial sales in the Roman Empire. It belonged to the family of indirect taxes that generated revenue without directly assessing a person’s land or wealth.

Emperor Augustus organized important Roman revenues after the civil wars, and taxes on commerce formed part of the imperial financial system. The centesima was collected through officials or tax contractors, depending on the period and location. Rates and practical enforcement could vary, so the simple one-percent description refers to the standard levy rather than every later arrangement.

It is often confused with the vicesima hereditatium, the five-percent inheritance tax, or the portorium, a customs charge. Those taxes applied to different taxable events.