Coemptio

Lat. Mutual purchase. One of the modes in which marriage was contracted among the Romans. The man and the woman delivered to each other a small piece of money. The man asked the woman, An sibi materfamilias esse vellet, whether she would become to him a mater' familias (mistress of his family); to which she replied that she would, {se velle.) In her turn she asked the man whether he would become to her a paterfamilias, (master of a family.) On his replying in the affirmative, she delivered her piece of money and herself into his hands, and so became his wife.

Adam* s Mom. Ant. 601. Cooper's Justinian, Notes *421.