To each of the principal temples, lands were annexed for the
maintenance of the priests. The estates were augmented by the
policy or devotion of successive princes, until, under the last
Montezuma, they had swollen to an enormous extent, and covered
every district of the empire.

And this concerning the frightful system of human sacrifices,
whereby the priestly caste maintained the prestige of its
divinities:

At the dedication of the temple of Huitzilopochtli, in 1486, the
prisoners, who for some years had been reserved for the purpose,
were ranged in files, forming a procession nearly two miles long.
The ceremony consumed several days, and seventy thousand captives
are said to have perished at the shrine of this terrible deity.

The same system appears in Professor Jastrow's account of the
priesthood of Babylonia and Assyria:

The ultimate source of all law being the deity himself, the
original legal tribunal was the place where the image or symbol
of the god stood. A legal decision was an oracle or omen,
indicative of the will of the god. The power thus lodged in the
priests of Babylonia and Assyria was enormous. They virtually
held in their hands the life and death of the people.

And of the business side of this vast religious system:

The temples were the natural depositories of the legal archives,
which in the course of centuries grew to veritably enormous