Originally, possessors of the princely title bore it as immediate vassals of the Empire, secular or ecclesiastical, who held a fief that had no suzerain except the Emperor. However, by the time the Holy Roman Empire was abolished in 1806, there were a number of holders of Imperial princely titles who did not meet these criteria.
Thus, there were two principal types of princes; those who exercised Landhoheit (sovereignty within one's territory) as well as an individual or shared vote in the College of Princes; and those whose title was honorary, the possessor lacking an immediate Imperial fief and/or a vote in the Imperial Diet. The first came to be reckoned as "royalty" in the sense of being treated as sovereigns, entitled to inter-marry with reigning dynasties. The second tier consisted of high-ranking nobles whose princely title did not, however, imply equality with royalty. These distinctions evolved within the Empire, but were codified by the Congress of Vienna in 1815 when it created the German Confederation and recognised a specific, elevated status (Standesherren or Mediatized Houses) for the mediatized princes of the defunct Empire.
The actual titles used by Imperial princes varied considerably for historical reasons, and included archdukes, dukes, margraves, landgraves, counts palatine, "princely counts" (Gefurstete Grafen), as well as princes. Moreover, most of the German fiefs in the Empire (except electorships) were heritable by all males of a family rather than by primogeniture, the princely title (or whatever title the family used) being likewise shared by all agnatic family members, male and female.
The estate of imperial princes or Reichsfürstenstand was first established in a legal sense in the Late Middle Ages. A particular estate of "the Princes" was first mentioned in the decree issued by Emperor Frederick Barbarossa in 1180 at the Imperial Diet of Gelnhausen, in which he divested Duke Henry the Lion of Saxony and Bavaria. About fifty years later, Eike of Repgow codified it as an emanation of feudal law recorded in his Sachsenspiegel, where the lay princes formed the third level or Heerschild in the feudal military structure below ecclesiastical princes. Officially the princely states of the Holy Roman Empire had to meet three requirements: