In Roman law, mancipatio (f. Latin manus, "hand"; and capere, "to take hold of") was a solemn verbal contract by which the ownership of certain types of goods (res mancipi) was transferred.
[1] Res mancipi were forms of property important in an early agrarian society: land, cattle, and slaves.
[2] The right of ownership (dominium) for such goods was reserved to Roman citizens, the original term for which was Quirites, and therefore called a "quiritian" or a "quiritary" right.
The procedure of acquisition of a slave as property "by scales and bronze" (per aes et libram) is described by Gaius as follows: "Mancipatio is effected in the presence of not less than five witnesses, who must be Roman citizens and of the age of puberty, and also in the presence of another person of the same condition, who holds a pair of brazen scales and hence is called libripens.
The purchaser, taking hold of the thing, says: Hunc ego hominem ex iure Quiritium meum esse aio isque mihi emptus esto hoc aere aeneaque libra ('I affirm that this slave is mine according to quiritary right, and he is purchased by me with this piece of bronze and scales').