Torture was a common practice in ancient Rome, especially during interrogations. Until the second century CE, torture was used only on slaves (with a few exceptions). After this period, torture also concerned the lower social strata. The slave’s testimony was considered true under Roman law only during torture. It was thought that they could not be trusted and that they had to be intentionally “tried” ¹. 

Some of the most common torture techniques used by ancient Romans include:

• Crucifixion: A form of death penalty used in ancient times, including by Persians, Romans, Phoenicians and Carthaginians, as a form of shameful execution on slaves, rebels and other non-full citizens. Only a low-level citizen (humiliores) could be sentenced to such death – in the event of a serious crime, e.g. betrayal of his own country. The convict was then tied or nailed to a large wooden cross and left there until his death. It was an unusually long and painful death ¹.
• Damnatio ad bestias: A form of capital punishment where the condemned person is killed by wild animals in front of a large audience in an arena. This punishment was usually reserved for those who committed crimes against the state or religion ¹.
• Boiling in oil: The victim was immersed in boiling oil until they died ².
• Molten gold poured down the throat: This method involved pouring molten gold down the victim's throat until they died ².
• Death by parasites: The victim was tied up and left outside to be eaten alive by insects and other parasites ².

Please note that these methods are extremely brutal and are not condoned by modern society.