Some Roman engagements were not official until what?

Several types of marriage ceremonies and betrothal contracts existed in ancient Rome. During the era of Emperor Constantine, a public kiss, or osculum, formed a legally binding engagement. Constantine decreed that if a sponsa (bride) died, the fiancé must return all gifts received from her family, regardless of whether or not the contract was officially sealed with a kiss. (See First Century Life: Hand In Marriage & Tie The Knot)

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