Although Paul doesn’t say where he was when he wrote Romans, there are substantial clues to indicate that he was in Corinth.

✏️In 15:25-27, Paul mentions that he has just collected donations from the assemblies in Macedonia and Achaia and intends to deliver them to the believers Jerusalem. Corinth was the capital of Achaia.
✏️In 16:23, Paul says that he has been staying at the home of Gaius who also hosted the local assembly. The same name is mentioned in 1 Corinthians 1:14 as a resident of Corinth.
✏️Also in 16:23, Paul sends greetings from “Erastus, the city treasurer”. A paving stone near the theater in Corinth and dating to the first century bears an inscription that reads “Erastus in return for his aedileship [position as magistrate—AP] laid [the pavement] at his own expense”.
✏️In 16:1, Paul introduces Phoebe, a deaconess of the assembly at Cenchrea, which was only a few miles from Corinth.