A Byzantine marriage ring!
The inscription says in Greek ΘΕ ΟΥ ΟΜΟΝΟΙΑ= God’s concord. A couple is depicted and between them a cross.
This ring is an example of the survival of pagan Roman ceremonial customs. In ancient Rome, marriage contracts were signed in front of the image of the emepror. After the 5th century its customary to depict Jesus Christ between the wedded couple.