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 12 A HISTORY OF THE CRUSADES 
was count of Poitou and duke of Aquitaine, but the offices were distinct.
 Each member of the feudal hierarchy had obligations to his lord and his
vassals. These obligations were defined by feudal custom. Whenever a dispute
arose between lord and vassal, it was settled in the lord's curia or court.
There the lord acted as presiding officer and the vassals rendered the decision.
In every fief the feudal custom for that fief was created by these decisions
in the lord's court. Thus feudal custom varied from fief to fief. Moreover,
in the eleventh century the formation of this custom was far from complete,
for questions were decided only when they arose and many came up but rarely.
Take for instance the customs governing inheritance. It was generally accepted
that if a man had sons, one of them was his heir, but in the eleventh century
the idea of primogeniture was by no means absolutely accepted. If the eldest
son looked unpromising as a warrior, the vassals felt free to choose one
of his younger brothers. If the two eldest sons were twins, the fief might
be evenly divided between them. When a man died leaving a son under age,
who cared for the fief and performed the service due from it? Sometimes it
was the nearest male relative on the mother's side, sometimes on the father's
side. In other fiefs the custody of minors belonged to the lord. But despite
the variations from fief to fief it is possible to make certain general statements
about feudal obligations that are reasonably valid. 
 The fundamental purpose of the feudal system was cooperation in war. Every
lord was bound to protect his vassal from enemies outside the fief and every
vassal owed military service to his lord. In some cases the vassal owed only
his own personal service; in others he was bound to lead a certain number
of knights to his lord's army. By the thirteenth century the military service
owed by vassals was carefully defined and limited, but this process was not
complete in the eleventh century. In most fiefs a distinction was made between
offensive and defensive campaigns and the length of time a vassal had to
serve in the former was limited — forty days was usual in the thirteenth
century. When the fief was in danger, obviously the vassals were bound to
stay in service as long as they were needed. Then the feudal system was political
as well as military. When there was a question of feudal custom to be decided,
the vassals were bound to obey the lord's summons to his court. Moreover,
as the vassals had a strong interest in the welfare of their lord and his
fief, they expected him to consult them before making an important decision.
When their lord was