1. An agreed payment for a thing or services specifically contracted for; rent, hire.
“There must be consent, a thing let, and an agreed payment (merces) …. The merces must be certain and Justinian’s texts say that, as in sale, it must be money. But there is not the same difficulty here, and Gaius does not state such a rule. It is possible that it did not exist in classical law and, even under Justinian, some cases cannot be reconciled with the rule. The rent of land might be in produce and even a fraction of the crop. This last conflicts with the rule of Gaius that it must be certain: it is held by some writers that the text is interpolated, by others that the relation was not really locatio conductio, but societas (partnership). The merces was not usually a lump sum: more often it was a series of periodical payments.” W.W. Buckland, A Manual of Roman Private Law 289–90 (2d ed. 1939).
2. A reward, esp. for a gratuitous service. Cf. HONORARIUM.“A recompense paid for any kind of services, without a preceding agreement (e.g., for saving one’s life) is also called merces.” Adolf Berger, Encyclopedic Dictionary of Roman Law 581 (1953).
