This system of immunity was greatly extended by the
Carolingian sovereigns, but with two important changes. (1) Henceforward the privilege
was seldom granted to laymen, but was bestowed as a matter of course on the
estates of bishops and of religious houses. (2) The holders of such
ecclesiastical estates were compelled to vest their powers of police and
justice in the hands of laymen (advocati) chosen either by the central
power or by some approved form of election. The intention of these changes was
to use the private courts for the maintenance of public order, to extract the
sting from a dangerous privilege, and to make it a serviceable instrument of
royal policy. But only one half of the scheme was permanent. By the middle of
the ninth century, when immunitas had been granted to all religious
foundations, the Carolingians allowed the right of choosing the advocati
to slip from their feeble grasp.
The privileged estates remained, but the royal
control over their internal government was gone. They became ecclesiastical
seignories; whatever checks were imposed upon the power of their rulers came
from the lay-nobles who were their neighbours, or from the subject population.
Partly from respect for custom and tradition, partly from motives of
self-interest, the great ecclesiastical landowners sided with the Crown, even
in the tenth century, when the fortunes of royalty were at their lowest ebb.
But for this support a price had to be paid; the old privileges were maintained
and even augmented by grants of the power of life and death (hautejustice,
blut-bann). Thus came into existence the class of ecclesiastical princes,
who throughout the Middle Ages maintained a state, and wielded a power,
comparable with that of any lay feudatory.
