Toward the end of that time, when he wrote the First Epistle to the Corinthians, the Apostle sent them greetings from Aquila and Priscilla. This means they were still there.
But about a year later, when he wrote this Epistle to the Romans from Corinth, he sends them greetings in Rome. This means they were already there.
They had returned after Claudius’s death together with other Jews. Among these were all those to whom Saint Paul sends greetings here.
The Apostle calls them his συνεργούς, fellow workers, because they helped him in the work of the gospel. Or, in general, they contributed to the conversion of the Gentiles, which Saint Paul regarded as his personal work.
Why did he not simply say, “my fellow workers,” but add, “in Christ Jesus”? It was so that no one would think he meant only their partnership in the craft, because they too were tentmakers, cf. Acts 18:3, says blessed Theodoret.
He speaks as though saying, “They helped me in word and teaching, and shared with me labors and dangers,” says blessed Theophylact.
An example of such cooperation is their guidance of Apollos toward a more perfect knowledge of the way of the Lord, or Christianity, see Acts 18:26. Of course, this was not the only example.