Nexum

Throughout Roman law there is a curious persistence of dual forms for the attainment of the same end which may be a survival of two distinct systems of customary law possessed by different peoples, the conquerors and the conquered.

and from these Real contracts he selects Mutuum, the contract which took the place of the old formal contract of Nexum, the source of Roman contract law.

As a form giving rise to an obligation Nexum was apparently a contract for a money loan (certa pecunia credita);

A definition which has descended to us from one of the Latin antiquarians describes nexum as omne quod geritur per æs et libram, “every transaction with the copper and the balance,” and these words have occasioned a good deal of perplexity.

It is unfortunate that we cannot track the early history of Contracts with the same absolute confidence as the early history of Wills, but we are not quite without hints that contracts first showed themselves through the nexum being put to a new use and afterwards obtained recognition as distinct transactions through the important practical consequences of the experiment.

Nexum, therefore, which originally signified a Conveyance of property, came insensibly to denote a Contract also, and ultimately so constant became the association between this word and the notion of a Contract, that a special term, Mancipium or Mancipatio, had to be used for the purpose of designating the true nexum or transaction in which the property was really transferred.