In the 11th and 12th centuries, a series of popes challenged the authority of European monarchies about who had the authority to appoint ("invest") local church officials such as bishops of cities and abbots of monasteries.
After the decline of the Western Roman Empire, investiture was performed by members of the ruling nobility despite theoretically being a task of the church. Many bishops and abbots were themselves usually part of the ruling nobility. Given that most members of the European nobility practiced primogeniture, and willed their titles of nobility to the eldest surviving male heir, surplus male siblings often sought careers in the upper levels of the church hierarchy. This was particularly true where the family may have established a proprietary church or abbey on their estate. Since Otto the Great (936–72) the bishops had been princes of the empire, had secured many privileges, and had become to a great extent feudal lords over great districts of the imperial territory. The control of these great units of economic and military power was for the king a question of primary importance due to its effect on imperial authority. It was essential for a ruler or nobleman to appoint (or sell the office to) someone who would remain loyal.
Since a substantial amount of wealth and land was usually associated with the office of a bishop or abbot, the sale of church offices—a practice known as "simony"—was an important source of income for leaders among the nobility, who themselves owned the land and by charity allowed the building of churches.