Most of Paul’s epistles were written to provide guidance to churches he had either founded or preached at while on his missions, but, oddly, Paul had never visited Rome and held no formal standing with the church. As he writes in Romans 15:22, “I was hindered these many times from coming to you,” and in Romans 1:11, “For I long to see you, that I may impart unto you some spiritual gift.”
Nonetheless, in Chapter 16 of Romans, Paul greets 28 people by name — several of whom were women. Based on the familiar tone with which he addresses these acquaintances, Paul had most likely met them before on a mission or in Jerusalem. Writing a letter to a group of people he had never met was unusual, but it’s assumed Paul at least had a tertiary relationship with the community in that region, even if — despite what the tone of his letter might imply — it was a church over which he had zero authority.
Some speculate the Epistle to the Romans was an “ambassadorial letter” by way of introduction (via “Antioch and Rome”), which could also explain the letter’s overly-formal tone in contrast with the other epistles he wrote. Paul, who was in Corinth at the time of the Epistle’s writing, did eventually visit the Roman church in person around 60 A.D., when he presumably met the letter’s recipients and most likely died there shortly after (via BBC News).