Bouvier's Law Dictionary, Revised 6th Ed (1856):

BENEFICIA. In the early feudal times, grants were made to continue only
during the pleasure of the grantor, which were called munera, (q. v.) but
soon afterwards these grants were made for life, and then they assumed the
name of beneficia. Dalr. Feud. Pr. 199. Pomponius Laetus, as cited by
Hotoman, De Feudis, ca. 2, says, " That it was an ancient custom, revived by
the emperor Constantine, to give lands and villas to those generals,
prefects, and tribunes, who had grown old in enlarging the empire, to supply
their necessities as long as they lived, which they called. parochial
parishes, &c. But, between (feuda) fiefs or feuds, and (parochias) parishes,
there was this difference, that the latter were given to old men, veterans,
&c., who, as they had deserved well of the republic, sustained the rest of
their life (publico beneficio) by the public benefaction; or, if any war
afterwards arose, they were called out, not so much as soldiers, as leaders,
(majistri militum.) Feuds, (feuda,) on the other hand, were usually given to
robust young men who could sustain the labors of war. In later times, the
word parochia was appropriated exclusively to ecclesiastical persons, while
the word beneficium (militare) continued to be used in reference to military
fiefs or fees.