Roman Jurisprudence

The Roman Empire has a handful of written laws(The Twelve Laws of Rome ), which govern the behavior of all individuals (both citizens and non-citizen residents) inside the Empire. Everyone is required to obey the law, and those who have violated the law, if caught, will be brought before the praetor of the city/town, or to the procurator/proconsul of the province, for a ruling. For civil cases (citizen-v-citizen lawsuits), the praetor appoints a judge, who is required to be of Patrician rank. If the crime involves a capital punishment of a Roman citizen or Freedman, it must be adjudicated by the governor of the province (proconsul/procurator). Peregrines and Provincials will have their cases heard by the Praetor of the municipality.
There are no juries, and appeals cannot be made except to the Emperor himself, who will almost never agree to hear the case.

Conviction

The Roman Empire does not have long-term prisons and there is no concept of "serving a sentence." Cells exist to temporarily house individuals either awaiting trial, or awaiting the carrying out of the sentence (which is usually either flogging or execution). Punishment for serious crimes is swift and final (i.e., fatal).

Possible sentences in Criminal Cases

There are five possible sentences in criminal cases which the judging party can impose upon someone found guilty of violating the law. Which sentence a person receives depends on the nature of the crime (i.e., minor crimes do not carry capital punishments), and also the Social Class in the Empire of the convict. For example, most crimes which would lead to execution for others will simply result in exile for a Patrician, and flogging cannot be administered to Roman citizens or Freedmen.
Fines are generally levied against Roman citizens (of all ranks) and Freedmen for minor violations, such as trespassing on private property or petty theft. The amount of the fine left to the judge. In the case of petty theft, if the item has been returned, the fine will usually be nominal. However, if the item cannot be returned (e.g., it was broken or sold to someone else and is now gone), the fine will be larger.
House arrest is a rare penalty that non-Patrician citizens and Freedmen may receive for violating the Imperial law against the public use of magic. The duration of this penalty is up to the judge, and will depend on the level of violation. Minor use of magic in public might result in a few days or a week of house arrest. Major use of magic in public would result in much longer durations (e.g., months).
Flogging is a penalty that may only be imposed on non-citizens (i.e., provincials, foreigners, and slaves). Even Freedmen are not allowed to be flogged. This penalty is generally imposed on non-citizens instead of fines or house arrest (or rather, those latter two penalties were put into place when flogging of Roman citizens was made illegal). Flogging is a painful form of torture -- the convict is not merely whipped a few times but is essentially beaten to within an inch of his life.
Execution is imposed for most major crimes such as murder, military desertion, or the torture of a Roman citizen. In many cases, a Patrician can request exile instead of execution, whereas others would be summarily executed. The manner of death is up to the judge, but also depends upon the class of the convict. Roman citizens are usually beheaded (which is seen as "merciful"), whereas slaves or foreigners will be crucified, thrown into the gladiatorial arena, or burned alive.
Exile is imposed on Patricians for most offenses (other than murder of a Roman or military desertion) rather than death, and on non-Patrician citizens for several lower offenses (such as murdering a non-Roman, which is seen as a less serious offense). Technically, the penalty for all these offenses is death, but the convict may request exile instead. Exile is seen as equivalent to death by Romans, who (mostly correctly) view life outside the Empire as likely to result in a quick death. In practice, hardly anyone fails to request exile when the alternative is death.