The letter to the Romans was written with great probability from Corinth. There are four reasons for that:
We do not know the exact date - but it is usually set between 55 and 58 AD.
Rome was the first city in the West to reach 1 million inhabitants, many of them living in poor conditions, coming from other regions of the empire. There was also strong presence of the Jews. Archeology confirms the presence of many synagogues in Rome in the first century AD.
At first, the Roman Church was composed of the large Jewish Christian membership and small but growing number of the Gentile Christians. But then, the emperor Claudius (around 49/50 AD), expelled all the Jews from Rome (see Acts 18:2). They could come back when the new emperor, the infamous Nero - the great persecutor of Christians - allowed them to come back in 54 AD.
So, for four years, the Gentile Christians had the time to develop their own structure and traditions, independent of the Jewish Christians’ influence. Then, the Jewish believers in Christ came back and the problems arose: divisions, looking down at each other, judgment, and so on. Thus, we have to situate this letter within this context.
The letter can be fairly divided into three parts:
The main theme of the letter is similar to that of the letter to the Galatians - justification. Yet, it is developed in a more logical and extensive way and in a less passionate manner than in Galatians.
Paul did not know the community of Rome personally, nor he was the founder of the Church in Rome. The Church’s tradition gives that credit to Saint Peter. But he knew many members of that Church, who he met during his missionary journeys - Prisca and Aquila, for example (see Rom 16:3; Acts 18:2–3), which gave him certain familiarity with the community and the problems they were facing living in the capital of the great empire.
Planning to spend some time in the community in Rome and then proceed to Spain for another mission (Rom 16:22–24), Paul took this opportunity to present to them the Gospel he preached or - to put it in his words, “as reminding them” (Rom 15:15) about the content of the true Gospel.