Imagine a society (medieval, but that isn't very important here) that has approved slavery. You can trade, buy, sell and hire slaves at will in the market.

Introduction

Slaves are usually "harvested" from indigenous villages that are attacked and conquered by the kingdom. Also, but not so common, people can sell their sons or even themselves to be slaves, usually if they are extremely poor (at least their new owners will usually take care of them, otherwise they will lose money). Another way to get slaves is during a war, war prisoners sometimes aren't returned to their homes after a war and they become slaves of the victorious empire, even this may happen with civilians in war zones.

The idea: Sell prisoners.

The thing that I want to add is the possibility of buying prisoners as slaves. This will have 2 main advantages:

• The government will spend less money on prisons.


• The slave market will have cheaper prices due a new and constant flow of slaves to the market (wars and indigenous villages aren't so common).

And finally, it may be a bit interesting.

It's quite understandable and obvious that slaves can be released. An owner can at will give freedom to its slaves, he just needs to sign a little contract that states the freedom of the person. Sometimes slaves perform deals with they masters if they work hard and without causing problems during X years they get freedom.

The problem

If you can buy prisoners as slaves and you can get them free at will, you can, as a rich person, member of a rich family, assains/thief guild, etc, perform a criminal activity, be jailed, be bought by a friend, and finally be released by him.

Basically, the law won't be any problem for rich or illegal organizations.

How can I prevent this problem but allow the sale of prisoners?

Even not allowing slaves to be set free by their masters it still being the same. You can be bought by a friend, family or guild and keep your life as normal. I don't want that.

Not much necessary to know

In this world, there is magic, some magic (usually healing magic) need life forces of victims to be performed. I want to let mages buy cheap prisoners and use them as life-force batteries to power they healing services in rich hospitals. I was thinking in prisoners because they are actually criminals, not just "slaved persons", so mages wouldn't annoy about kill them to fuel their magic, also, they may be cheaper.

A solution could be to not buy the prisoner, just it life-force. A mage visits a prison, ask for some life-force, pay the price, guards transfer the prisoner to a special room, and there part of its life is taken away from him to a jar by the mage. Simple, easy and effective. But I don't like much the idea. I would like the idea of buy prisoners as assets, not just their life essence.

All prisoners are propierty of the Government during their condemn. The "owners" don't buy them, just hire them for long periods.

In a medieval society, because condemns need to be really harsh, you need to use those slaves only for the most dangerous jobs, like rowing ships, working in mines, etc. If not, people will commit crimes and then ran away during their slavery time, because the Government has almost no security forces and just by traveling 100 km nobody knows you.

It used to commonplace

The question show a misconception about pre-modern societies. They were not modern societies in which people dressed funny and had a handful of unusual laws; they were profoundly alien. As it is said, the past is foreign country.

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  First of all, in pre-modern societies they had no concept of imprisonment as a form of punishment. Misdeeds were of only two kinds: most of them incurred some sort of fine, or price, to be paid; the others called for the capital punishment.

  
  
  

  What exactly qualified for capital punishment varied from place to place and from time to time. Murder was a capital crime in the classical world, but not so much in the early Germanic Middle Ages, where it called for payment of a man-price, or weregild. On the other hand, all pre-Renaissance penal codes were very harsh on adultery and other forms of domestic treason.

  
  


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  Enslavement was a form of capital punishment.

  
  
  

  The Romans called it capitis deminutio maxima, the greatest diminishment of the head. In early Rome, it involved selling the convict across the border, trans Tiberim, on the other side of the river Tiber. In more civilized times, it involved usually making the convict a slave of their punishment, servus poenae, and selling them to work in a mine, damnatio ad metalla.

  
  
  

  The point is that it was a capital punishment. (Capital from caput, head.) The person was legally dead. Their wealth was either confiscated or passed to their heirs. They could not come back from the dead, and enslavement was assimilated with death, servitus morti adsimulatur.

  
  
  

  Even if they were miraculously set free (which was usually not possible, because they were branded before being sold, and branded slaves could not be manumitted), they had no family, no relations. Wait, a modern person will say, but this was a legal fiction; of course their natural family would recognize them. Nope, not so; the past is a foreign country, and the Romans tooks family very seriously, and would never welcome an unrelated former convict.

  
  


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  Were the Romans the only one to practice penal slavery?

  
  
  

  No, not at all.

  
  
  

  In early medieval Hungary,

  
  
  

  
  

  Freemen could be sold into slavery for numerous crimes. Any common woman (plebeia) caught in adultery would be sold 'without the hope of freedom' (sine spe libertatis), and the same fate awaited a common man caught in the same sin.

  
  
  

  (Cameron Sutt, Slavery in Árpád-era Hungary in a Comparative Context, BRILL, 2015, ISBN 9789004301580)

  
  

  
  
  

  In some western European countries, early Germanic penal codes had similar provisions.

  
  
  

  In medieval China they sold the convicts far away, in the poor provinces at the margins of the empire.

  
  
  

  The early modern English sold them across the ocean, in America.

  
  


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  But what about the rich? And their goons?

  
  
  

  The rich were rich anyway. The rules did not apply to them. A rich Roman (or a rich Chinese) could never be enslaved or God forbid! executed; the worst of the worst was exile (which implied loss of property) but this was exceedingly rare, the usual maximum punishment for a rich criminal being relegation (sort of like exile, but without complete loss of property).

  
  
  

  And their goons? Well, rich people did not stay rich by spending money on slaves which they intended to manumit immediately, not to mention that it would have been against social decorum to do that; and in a pre-modern society, loss of face (or, as they called in Europe, dishonour) was to be avoided at all costs.

  
  

Just like in real life, you could use parole officers to ensure the prisoners are being subjected to the punishments your government believes they should receive. Although real-life parole officers are more focused on the prisoner's background and activities outside of prison, your parole officers will be more focused on the buyer.

Before making the purchase, the buyer must agree to uphold whatever punishments/type of work/treatment that the prisoner should receive, and how long they will remain a prisoner(assuming it isn't for life). Upon buying a prisoner destined for slavery, the buyer must register themselves(if it's their first time) and the prisoner with the nearest parole officer/parole office. These officers will typically be part of your government's normal police/military jurisdictions.

After registering, the buyer will be subjected to periodic, and ideally random, inspections of the prisoner-turned-slave's working conditions. If the parole officer is suspicious that the buyer is not adhering to the conditions they agreed to before the purchase, the officer can issue warnings and set up more thorough, and again random, investigations.

Should the buyer be found beyond a reasonable doubt to be treating the slaves better/worse than they should, then the slave may be taken away from the buyer without compensation. Repeated or particularly egregious offenses, such as killing, maiming, or releasing them, could result in a complete ban from further purchases.

Basically, the law won't be any problem for rich or illegal organizations.

How can I prevent this problem but allow the sale of prisoners?

I think you could solve or mitigate this problem by thinking over who owns a newly-convicted prisoner by default.

In cases where it's the government of the day, they may have some good reason to not sell a criminal kingpin out of jail. There are some parallels between this and modern parole.

On the other hand, you could set up the system so that, for example, the surviving family of a murder victim decides if, and at what price, the convicted murderer can be "bailed out" of jail and into slavery. There may still be problems of duress, but at least they might be interesting ones.

On the final hand, "the law isn't a problem for the rich" isn't exactly unique to your situation.

There is no such thing as personal property

The kingdom is an absolutist monarchy, along the lines of Pharaonic Egypt, Imperial China, or Achaemenid Persia. The king 'owns' everything in the country. If you have money or power, then you can pay the God-king for his material favors, or they could be granted to you as a divine boon.

But, there is no concept of 'ownership' at all. Everything that is, belongs to the God-king; the best anyone else can hope for is the right of possession (which could of course be revoked by the king at any time).

In this way, slaves are the property of the king, as is everything; but right merchants, guilds, lords and sundry can pay the king for the right to tell these slaves what to do.