Who wrote Romans:

Like many books of the New Testament, the book of Romans was a letter written to a church. In this case, the Apostle Paul was writing to a group of Christians within Rome. While Paul’s authorship of Romans is rarely contested, some have questioned how Paul, who at the time of the writing of the letter had not yet visited Rome, knew so many members of the Roman church.

The most likely answer is Paul met the 26 members listed in chapter 16 prior to them moving to Rome or while the members were in exile from Rome. Two members of the Roman church, Pricilla and Aquila, are greeted in chapter 16:3-5. According to the book of Acts, Paul traveled with Pricilla and Aquila from Corinth to Syria (Acts 18:1-2, 18) while the couple was in exile from Rome. Although we cannot definitively link any other members listed in Chapter 16 to Paul’s ministry, we can conclude he likely met them under similar circumstances as Pricilla and Aquila.