I know the Romans had a Law system the influenced Western Law, which implies they had a police force of some type.
Did they just use regular soldiers who were stationed at the local garrison? Did they have detachments they used for this? And was this the same in the provices?
“Law” does not imply “police”. Police forces in the sense that we have them are a modern invention – early nineteenth century, if I recall correctly, in the UK. Probably later in the US. Law is much older than that.
The Romans had no police force. They had an army, of course, and the army would where necessary enforce the law in the interests of the state (or, for that matter, flout the law in the interests of the state).
But the army wasn’t interested in private disputes between citizens. You had a dispute with your neighbour – e.g. you accused him of stealing your cattle, or trespassing on your land - you went to court. If you got a judgment in your favour, it was up to you to enforce it. If all else failed, you could enforce it by force, or you could hire some heavies to do it for you. If you didn’t have the strength or the money to enforce your judgment, tough. You were then dependent on social and cultural pressure, or the goodwill of a more powerful or wealthier friend. Hence the “client” system.
That may have been true during the Republic, and indeed it probably remained true of many provincial towns. But the emperor Augustus created a police force in Rome, along with a fire department. An out-of-copyright book available online has a chapter about the police and fire departments of imperial Rome.