Question: What was the punishment for stealing something in ancient Rome?
Roman law, including the laws for theft ("furtum"), changed quite a bit over the course of history. Under the oldest known law code, the Twelve Tables, the laws differed somewhat depending on whether the person was a slave or a free man. A free man was generally flogged and given into slavery to the person whose property he took, while a slave would be beaten then executed. If you were to be caught stealing at night and killed, the killer would not be punished. If it was during the day, then you were allowed to try to physically stop the thief, but you were allowed to kill that person only if he try to defend himself.
What eventually developed in Roman law was a distinction between criminal and civil law. If someone's property were taken, the state would issue a punishment and the person could bring a lawsuit against the thief. In the case of a slave or non-citizen, it seems that flogging and execution were still common punishments, while most citizens could expect to repay the victim for the stolen item two to four times its original value. The thief also might be sued, particularly if the victim could show that the item is irreplaceable or that not having for a time caused damage (such as a plow that was stolen during harvest).
It is easy to see that Roman law provided the basis for our laws, which also depend on civil and criminal penalties. Roman law also tended to be somewhat flexible, and the penalties were decided on a case-by-case basis - although the court always needed to point to a precedent in which a similar case was decided in the same way.