Heidegger's Bible Handbook: 2 Thessalonians: Time of Writing

3. The time of writing. That it was written after the former Epistle, and a long time after the principate of Gaius Caligula, is asserted against Grotius.

Hugo Grotius

It appears to have been written not long after the former Epistle, as Baronius has rightly observed out of Chrysostom and Theodoret, with good reason rejecting the opinion of Saint Athanasius, who asserted that the Epistle was written at Rome. It also appears to have been sent from Corinth, after Timothy had returned there to Paul from Thessalonica. But we have already noted above the opinion of Grotius, making this Epistle earlier than the first, referring it to the time of the principate of Gaius Caligula,[1] and all the most learned have marked it as an error. Certainly in the times of Caligual the Thessalonians were yet unknown to Saint Paul, and were not yet converted to the faith of Christ; since in the final year, that is, the fourteenth year, of Claudius,[2] he visited them, and gave them their initial instruction in the Christian faith, Acts 17:1, etc. Before which time, that there were not believers at Thessalonica, is sufficiently apparent from Acts 17:4. For, if there had already been believers there, Paul would have taken them as companions, and visited the Synagogue with them.

[1] Caligula reigned as Roman Emperor from 37 to 41. [2] Claudius reigned as Roman Emperor from 41 to 54.