I can try to explain what might happen in the the Middle Ages (emphasis on “might” since there are a lot of possibilities…)

First of all, modern “eminent domain” basically means the landowner can appropriate or expropriate the land, especially for public use - to build a road for example (so it’s also called appropriation or expropriation, or “compulsory purchase” even though it really means compulsory sale). However, the landowner needs to compensate whoever is currently using the land.

The biggest difference between the Middle Ages and now is that the landowner is now often the “state”. A government acts as a sort of abstract corporation that owns the land, whether it’s a local municipal government or a federal government, or a monarch (at least in Canada, we call this “crown land”, since it theoretically all belongs to the Queen.)

This definition of eminent domain didn’t really exist before the 17th century. In medieval Europe there was no abstract concept of a “state” like this. We have this concept now thanks to Hugo Grotius - the state is a thing, it has clear borders, all the land inside of those borders are owned by the state, i.e. the state has eminent domain.

Of course medieval people did have a concept of property ownership, just not quite like this. Someone owned some land, and either they or someone else was actually using it. There was also land that wasn’t owned by anyone but could be used by everyone (commons), and land that wasn’t owned or used by anyone (waste land).

I can’t pretend to give a standard answer for everywhere. There was a mishmash of laws and customs in different parts of Europe at different time periods. In the the central/later Middle Ages (let’s say, the 12th century and later), medieval people generally borrowed the concept of “dominium” from Roman law. For the Romans all dominium/domain rested with the owner, it didn’t matter if the property/land was held or being used by someone else. Medieval law developed it further, distinguishing between direct domain (dominium directum) and useful domain (dominium utile).

Some medieval legal texts developed a theoretical framework, for example the Siete Partidas, compiled by Alfonso X of Castile in the 13th century:

Moreover, we decree that when an emperor desires to take lands, or any other property, from any person, either for himself, or to give it to some one else; although he is lord of all those in the empire in order to protect them from violence, and preserve them by justice, he has nevertheless no authority to deprive anyone of his property without his consent, unless he does something on account of which he should lose it by reason of law. And where it happens that the emperor was compelled to take it, for the reason that he had need to make disposition of it for the common benefit of the country, he is required by law to give beforehand something in fair exchange for said property which is worth as much, or more, so that the owner is remunerated in the sight of all good men. (Siete Partidas, Part II, Title I, Law II, pg. 270)

This is the top-down perspective of an “emperor” (Alfonso X was “only” king of Castile but fancied himself an emperor). It was among the monarch’s duties to protect his subjects’ property and not deprive them of it without just cause and without just compensation.

Other than the king there might also be lots of different kinds of landowners. In more rural areas like in northern France, big landowners would be the nobility who had agricultural land, castles in the countryside, etc., or the church, which owned churches, abbeys, chapels, and so forth, as well as the land surrounding them. “The church” was almost like a modern corporation, although ownership really rested with the individual (the local bishop or abbot for example). Ecclesiastical and secular property could include elements like ponds, mines, salt marshes, forests, or any other land that could be economically useful.

Louis IX of France also included something similar in his own law codes, but from a more local perspective:

On seizing and holding a commoner's lodging: If a gentleman wanted to build a residence and his commoner had a piece or two of land he held from him, the lord can take them, if he wants, to build on, by making a fair exchange, to make either a pond, or a mill, or another dwelling. (Établissements de Saint Louis, ch. 98, pg. 64)

So what does that really mean in practise…well, the church and the nobility loved making charters where each party’s rights were set out in detail. Land could be bought and sold, and the party with direct domain had certain rights, and the party with useful domain had certain rights, depending on the terms of the charter. So, say the local nobleman owned a fish pond and the fishermen living around the pond catch and sell the fish - some percentage of the profits go to the local lord with direct domain. He could sell or transfer his domain to someone else but the fisherman still had their useful domain (i.e., the new boss isn’t going to replace them with new fisherman).

I can give an example from something that has come up in my own research: in the 12th and 13th centuries the dukes and duchesses of Brittany (northwestern France, but technically independent at the time) wanted to build a new defensive wall in the city of Nantes. For the most part this involved rebuilding the old Roman wall, but they needed to expand it and had to expropriate some more land, especially from nearby churches and abbeys. Various charters confirm that the dukes and duchesses paid compensation to the bishop or the abbot/abbess affected - either in cash, or in exchange for a different piece of land, or by giving them rents and taxes from another property.

Guy of Thouars, Duke of Brittany…We wish to bring it to the attention of all that we have granted the Bishop of Nantes seven pounds in cash, in compensation for the loss of his orchard that he incurred due to the construction of a moat… (Everard, pg. 153)

Nantes is a city in the north, but in more urbanized areas, like the bigger cities in southern France (or in Flanders, or Italy), the church also owned a lot of property, as did the nobility, if there was a castle or other fortifications in the city for example. But more likely, houses and shops would be owned by wealthy burgenses (where we get the word “bourgeois”) and they would rent it out to others.

Owners and renters also loved making charters too, or contracts in this case. I mentioned above that it’s hard to give a general answer because the rights of the owner/user depended on whatever they agreed to in their contract, and that could vary wildly from contract to contract. Say the landowner owned a house and rented it out, but then decided to knock down the house and build something else. If the renter brought a lawsuit to the local town tribunal, the court would probably (maybe not 100%, but probably) side with the renter. Useful domain was felt to be more important than direct domain.

Hopefully that helps a little bit…it really depends on a ton of different factors that can change depending on time and place, and depending on the circumstances of the contract/charter. But generally, there was the concept of “domain”, and the person who was actually using the land probably couldn’t be dislodged from it very easily. If the landowner wanted to use the land in a different way, fair compensation needed to be paid, just like today.

Sources:

My main source is a book that has been conveniently written on this very subject!

Susan Reynolds, Before Eminent Domain: Toward a History of Expropriation of Land for the Common Good (University of North Carolina Press, 2014)

The primary sources I quoted are:

Judith Everard and Michael Jones, The Charters of Duchess Constance of Brittany and Her Family, 1171-1221 (Boydell, 1999)

Samuel Parsons Scott and Robert I. Burns, Las Siete Partidas, Volume 2: Medieval Government: The World of Kings and Warriors (University of Pennsylvania Press, 2001)

F.R.P. Akehurst, The Établissements de Saint Louis: Thirteenth-Century Law Texts from Tours, Orléans, and Paris (University of Pennsylvania Press, 1996)