A.T. Robertson Commentary Romans 16:23

"Gaius my host, and of the whole church, saluteth you. Erastus the treasurer of the city saluteth you, and Quartus the brother." — Romans 16:23 (ASV)

Gaius my host (Γαιος ο ξενος μου). Perhaps the same Gaius of 1 Corinthians 1:14 (Acts 19:29; Acts 20:4), but whether the one of 3 John 1:1 we do not know. Ξενος was a guest friend, and then either a stranger (Matthew 25:35) or a host of strangers as here. This Gaius was plainly a man of some means as he was the host of all the church. Erastus (2 Timothy 4:20) was "the treasurer of the city" (ο οικονομος της πολεως), one of the outstanding men of Corinth, the "steward" (housemanager) or city manager. See Lu 12:42; 16:1. He is probably the administrator of the city's property.

Quartus (Κουαρτος). Latin name for fourth.