What is the wedding vow that signifies shared identity?

The correct answer is the wedding vow "Quando tu Gaius ego Gaia," which is a traditional Roman wedding formula. This phrase translates to "When you are Gaius, I am Gaia," indicating a shared identity of the couple. In ancient Roman culture, this vow symbolized the merging of two lives into one unit and reflected the deep connection and commitment between the husband and wife.

This vow illustrates how Roman weddings were not just personal commitments but also communal recognitions of the bond being formed; it was critical in formalizing the identity of both partners within the institution of marriage. The names Gaius and Gaia were commonly used in this context, representing a typical Roman man and woman, thus making the vow relatable to the society at large.

In contrast, other options like Sponsalia refer to the betrothal or engagement period and do not signify the shared identity that is established in marriage. Usus pertains to a form of marriage based on cohabitation and is not directly a vow. Contubernium refers to a form of domestic partnership that may not involve formal marriage and does not encapsulate the same level of commitment as the shared identity expressed in the wedding vow.