Trinity ring symbols from the catacombs...

Above is the oldest, known symbol depicting the Holy Trinity by Christians in Rome. It was discovered in the catacombs.

       The first place to be referred to as catacombs was the system of underground tombs between the 2nd and 3rd milestones of the Appian Way in Rome, where the bodies of the apostles Peter and Paul, among others, were said to have been buried. The name of that place in late Latin was catacombae, a word of obscure origin, possibly deriving from a proper name, or else a corruption of the Latin phrase cata tumbas, "among the tombs". The word referred originally only to the Roman catacombs, but was extended by 1836 to refer to any subterranean receptacle of the dead, as in the 18th-century Paris catacombs. All Roman catacombs were located outside city walls since it was illegal to bury a dead body within the city, providing "a place…where martyrs tombs could be openly marked" and commemorative services and feasts held safely on sacred days. Read more...

Catacombs are human-made subterranean passageways for religious practice. Any chamber used as a burial place is a catacomb, although the word is most commonly associated with the Roman Empire. Above and below are Holy Trinity symbols found in the Roman catacombs made by early Christians. The symbol directly above was labeled "passim".

Scriptural References for The Above Trinity Rings:

• "May the grace of the Lord Jesus Christ, and the love of God, and the fellowship of the Holy Spirit be with you all." 2 Corinthians 13:14 (NIV)
• "For to us a child is born, to us a son is given, and the government will be on his shoulders. And he will be called Wonderful Counselor, Mighty God, Everlasting Father, Prince of Peace." Isaiah 9:6 (NIV)
• "Therefore go and make disciples of all nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit,  and teaching them to obey everything I have commanded you. And surely I am with you always, to the very end of the age." Matthew 28:19 (NIV)