A more thorough explanation:

Definition: Coemptio (koh-emp-shee-oh) is a type of civil marriage in ancient Roman law where the husband "purchased" the right to exercise marital power over the woman from her father through a fictitious sale.

Coemptio was a formal procedure where the father of the woman sold her to the husband in the presence of five adult Roman citizens and a balance-holder. The sale was fictitious, and the husband was called the coemptionator or coemptioner. This type of marriage gave the husband the power to control the woman's property and make decisions on her behalf.

The importance of coemptio as a method of civil marriage declined by the end of the Republic period.

Example: In coemptio, the husband would pay a sum of money to the father of the woman, and the father would sell his daughter to the husband. The sale was not real, but it gave the husband the right to control the woman's property and make decisions on her behalf.

Explanation: This example illustrates how coemptio worked in ancient Roman law. The husband would "purchase" the right to control the woman's property and make decisions on her behalf through a fictitious sale. This type of marriage was formal and required the presence of five adult Roman citizens and a balance-holder.