The Free Imperial knights (German: Reichsritter Latin: Eques imperii) were free nobles of the Holy Roman Empire, whose direct overlord was the Emperor. They were the remnants of the medieval free nobility (edelfrei) and the ministeriales. What distinguished them from other knights, who were vassals of a higher lord, was the fact that they had been granted Imperial immediacy, and as such were the equals in most respects to the other individuals or entities, such as the secular and ecclesiastical territorial rulers of the Empire (margraves, dukes, princes, counts, archbishops, bishops, abbots, etc.) and the Free Imperial cities, that also enjoyed Imperial immediacy. However, unlike all of those, the Imperial knights did not possess the status of Estates (Stände) of the Empire, and therefore were not represented, individually or collectively, in the Imperial Diet. They tended to define their responsibilities to the Empire in terms of feudalized obligations to the Emperor, including personal service and strictly voluntary financial offerings paid to the Emperor himself.
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To protect their rights and avoid vassalage to more powerful nobles, they organized themselves into three unions (Partheien) in the late 15th century and into a single body in 1577, and fought to win recognition. This status, beholden only to the Emperor himself rather than through a more powerful noble, meant the Imperial Knights were "immediate subjects" (their fealty was unmediated by another lord). As such, the Imperial Knights exercised a limited form of sovereignty within their territories.
The Imperial Knighthood was a regional phenomenon limited to southwestern and south-central Germany—Swabia, Franconia and the Middle Rhine area—zones which were highly fragmented politically and where no powerful states were able to develop. In northern and northeastern Germany, as well as in Bavaria and the Archduchy of Austria, the local nobles, facing larger states and stronger rulers, were incapable of developing and maintaining their independence. They formed the territorial nobility.
The immediate status of the Imperial Knights was recognized at the Peace of Westphalia. They never gained access to the Imperial Diet, the parliament of lords, and were not considered Hochadel, the high nobility, belonging to the Lower Nobility.