Roman Estates and Medieval Manors
The cornerstone of feudal economic power was the manor. This was an area over which the overlord exercised legal and economic control. The legal power was granted by the king, the noble acted as police force and court system. The economic control was derived from ownership of key facilities. The flour mill was a popular one, as were mines, iron works, looms, breweries and the like. The noble exated fees for the use of these facilities and, most importantly, did not allow any competing facilities to be set up (unless a stiff fee were paid for the privilege.) The monopoly power was very lucrative, although the weight of custom usually prevented excessive price exploitation. The noble also had the power to collect fees for a wide range of activities, ranging from funerals to gathering firewood in the forest.
When the Germans came into the France, Italy and other parts of the Roman empire, they found what would become "the manor system" already operating as "the estate system ." The Romans had also depended on agricultural activity for the basis of their economy. Since the end of the Punic Wars in the 2nd century BC, land ownership in Rome was increasingly concentrated in a small number of families. These lands were organized into estates, which were, as much as possible, self-sufficient. Early on, the Romans used slaves as their primary source of agricultural manpower. But the Roman custom of freeing slaves for faithful service eventually populated the estates with free men who turned into serfs over the centuries.
As with so many other Roman things the Germans found, they adopted the estate system as their own, and it became the basis of Medieval economic life.