From Academic Kids
A vassal or liege, in the terminology that both preceded and accompanied the feudalism of medieval Europe, is one who enters into mutual obligations with a lord, usually of military support and mutual protection, in exchange for certain guarantees, which came to include the terrain held as a fief. In fully-developed vassalage, a commendation ceremony, composed of homage and fealty with solemnity adapted from formulas of Christian sacraments eventually made its appearance. Such elegant refinements were not in evidence at the outset, however. At the commendatio, "the vassal thereupon fell under the charismatic power, pagan in origin, of the lord: his mundeburdium or mainbour, true power, at once possessive and protective" (Rouche 1987, p 429). Under the influence of the "mainbour" all previous social differentiations fell away, in a restructuring of social obligations that was radically new (Rouche 1987 p 429ff).
The development of the vassal, in a society that was increasingly organized around the concept of "lordship"— in French the seigneur— provides one of the threads by which the onlooker can see the Early Middle Ages evolving out of Late Antiquity. Lordship is the basic social institution of the uprooted Germanic societies, as Tacitus described them in Germania and the Roman West experienced them firsthand in the Migrations Period. The irreducible unit within these "tribes", which were in fact often assemblages of mixed culture (see Alamanni), was the comitatus or gefolge, "the Germanic war band as described by Tacitus and in Beowulf... based on the loyalty of warriors to their chieftain." (Cantor 1993 p.197) A similar Roman institution, in the social disorder of the 5th and 6th centuries, was the patrocinium, commonly translated by the French term "clientage". The courtlike followers who gathered of a morning in the hall of a great Roman personnage in the early Empire had devolved into a gang of young "enforcers" grouped round the charismatic figure of a patricius. This word too had changed from its more familiar original meaning, now to denote a military commander: the careers of Stilicho or Aëtius give examples of a patricius of the 5th century. By contrast, an apparent comparable example from the East, like the general Belisarius, still bore the aura of imperial legitimacy that the Western warlords could afford to ignore.
As the system developed in the seventh century, the vassals were gangs of freemen who voluntarily subjected themselves, in some varying degree of formality, to the authority of a leader, from whose distribution of loot they could expect to be fed, clothed and armed. The quality of a vassal was only in his fighting ability and the strength of his loyalty. The etymology of "vassal" is from a Celtic word gwas "boy" that designated a young male slave, with a Latinized form, vassus that appeared in Salic Law (Rouche 1987 p 429), not unlike the derivation of "knight" from Old English cniht and cognates in Frisian and Dutch, all meaning "lad"  (http://www.etymonline.com/index.php?l=k&p=3).
All later connotations, of chivalry, of aristocratic lineage and even of land-holdings have to be set aside: the original vassals were as mobile as their lords, a retinue of sworn bodyguards, whose status was a reflection of the status of their lord. The Merovingian kings of the 7th century dignified their personal retainers as antrustiones (Cantor 1993, p.198). In an earlier age, Alexander's bodyguard of generals were similarly singled out as his "companions." The various meanings of peer (French paire) still retain some sense of this original parity among equals who followed the charismatic leader.
Charlemagne's later developments connected vassals with the rewards of land, the only form of generating wealth, in a slow process, connected with the unfolding of the agricultural institutions called "manorialism" and the social and legal structures labelled— but only since the 18th century— "feudalism". It was a slow process that unfolded at different natural rhythms in various regions. In Merovingian times, only the greatest and most trusted vassals would be rewarded with lands. Even at the most extreme devolution of any remnants of central power, in 10th century France, the majority of vassals still had no fixed estate (Ganshof 1964).
The stratification of a fighting band of vassals into an upper group composed of great territorial magnates, strong enough to ensure the inheritance of their benefice to the heirs of their family, and a lower group of landless knights attached to a "count" or "duke" might roughly be correlated with the new term "fief" that was superseding "benefice" in the 9th century. The social settling out process also received impetus in fundamental changes in conducting warfare. As the example of the Huns demonstrated to the Romanized world that cavalry superseded a melee of fighting men on foot in determining the outcome of battles, the cost of maintenance of a mounted and increasingly armored fighting force was inflated. A mounted vassal needed wealth to equip the band of mounted fighters he was under obligation to contribute to his lord's frequent disputes, and wealth, where a money economy had disappeared, was only to be found in land and its productions, which included peasants, as much a resource of the land as wood and water.
- Cantor, Norman, The Civilization of the Middle Ages 1993
- Ganshof, François Louis, Feudalism translated 1964
- Rouche, Michel, "Private life conquers state and society," in A History of Private Life vol I, Paul Veyne, editor, Harvard University Press 1987 ISBN 0-674-39974-9de:Vasall