levying distraints. The owners were obliged to surrender any person
accused of a grave crime, but otherwise did justice at their pleasure.

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.