at legacy on which I do not need to
dwell. _Sacramentum_, on the other hand, needs a word of explanation.

_Sacramentum_ in Roman public law meant (1) a legal formula (_legis
actio_), under which a sum of money was deposited, originally in a
temple,[983] to be forfeited by the loser in a suit. The deposition _in
loco sacro_ gives the word to the process, and helps us to see that it
must mean some act which has a religious sanction. So with (2) its other
meaning, _i.e._ the oath of obedience taken by the soldier, who was
_iuratus in verba_, that is, sworn under a formula with a religious
sanction attached.[984] It is tempting to suppose that it is through
this channel that it found its way into the Christian vocabulary--the
soldier of Christ affirming his allegiance in the solemn rites of
baptism, marriage, or the Eucharist. It is a curious fact that it seems
to be used in this way in the religion of Mithras,[985] which was
especially powerful among the Roman legions of the Empire, and in which
there was a grade of the faithful with the title of _milites_.
_Sacramentum_ was here the word for the initiatory rites of a grade. In
the earliest Christian writers of Latin it usually means a mystery; thus
Arnobius writes of the Christian religion as revealing the "veritatis
absconditae sacramenta";[986] but in another passage the idea in his
mind seems to be that of military service. It is better, he says, for
Christians to break their worldly contracts, even of marriage, than to
break the _fides Christiana_, "_et salutaris militiae sacramenta
deponere_;"[987] and Tertullian more than once attaches the same
military meaning to it: "Vocati sumus ad militiam Dei vivi iam tunc _cum
in verba sacramenti spopondimus_."[988] Perhaps we may take it that the
word, though of general significance for a religiously binding force
produced by certain mysterious rites, had a special attraction for
writers of the painful third century A.D., as reflecting into the
Christian life from old Roman times something of the spirit of the duty
and self-sacrifice of the loyal legionary. In any case we have once more
a verbal legacy of priceless value.[989]

To sum up what I have been saying, there were certain ingredients in the
Roman soil, deposits of the Roman religious experience, which were in
their several ways favourable to the growth of a new plant. There were
also certain direct legacies from the old Roman religion, of which
Christianity could d