Greek: Κούαρτος —transliteration: Kouartos —Latin: Quartus —meaning: fourth —occurrences: 1 (Romans 16:23)
Timothy my [Paul’s] fellow worker greets you, and so do Lucius and Jason and Sosipater, my kinsmen. I, Tertius, who wrote this letter, greet you in the Lord. Gaius, host to me and to the whole church, greets you. Erastus, the city treasurer greets you, and Quartus, the brother. [The grace of our Lord Jesus Christ be with you all. Amen.] —Romans 16:21-24 LSB
As this is the only mention of Quartus, it is not completely clear whether he was a physical brother of Erastus or more likely a brother in the Christian sense (a fellow Believer), or possibly both.
The New International Version translates this as “our brother Quartus” (Romans 16:23 NIV).
Eastern Orthodox tradition says that Quartus was born in Athens, Greece, and was a wealthy noble. They say that after his conversion, he became a great evangelist, the bishop of Berytus (now Beirut, Lebanon) and eventually died a martyr in Athens (tortured, stoned and burned).