A more thorough explanation:

Term: Sponsion
Definition: Sponsion is a formal promise made by a person to become a surety. It can also refer to a promise made by an official agent that requires later approval by their superior. In Roman law, it is a type of guarantee that only Roman citizens could make.
Examples: If you promise to pay back a loan for your friend, you are making a sponsion to become a surety. During wartime, a general may make a sponsion to an enemy, but it needs to be approved by their superior before it becomes valid. In ancient Rome, only citizens could make a sponsion to guarantee an oral contract.
Related Word: Sponsional (adjective)