The apostle Paul regarded Jerusalem as the center of his travels. In his letter to the Romans, he wrote, “So that from Jerusalem and round about unto Illyricum, I have fully preached the gospel of Christ.” Romans 15:19. Illyricum lay to the north-west of Macedonia, and its border was the nearest place he had been to Rome at that stage of his career. It does not appear that he actually entered Illyricum, but only approached it.
It is clear from Romans 1525,26 that the Roman letter was written from Corinth, during the apostle’s third missionary journey, just before he went to Jerusalem for the last time. The addition to the letter suggests that it was taken to Rome by Phoebe, and this may well have been the case. (See Romans 16:1).
Illyricum is not mentioned in the Acts of the Apostles, and therefore the reference to the place in Romans 15:19 cannot have been copied from the Acts. Nevertheless, it is possible to show how accurate is the statement in the Epistle. Acts 20 describes what happened after the apostle’s stormy experience in Ephesus in Asia Minor. Verses 1 and 2 read, “And after the uproar was ceased, Paul called unto him the disciples, and embraced them, and departed for to go into Macedonia. And when he had gone over those parts and had given them much exhortation, he came into Greece. (this was the apostle’s second visit to Greece). In going over the parts of Macedonia, the apostle would have come near the borders of neighboring Illyricum.
The case is strengthened by reference to the question of time. Paul, as already stated, had been to Greece before (Acts 16:12-18:1). His journey then, however, was confined to Eastern Greece—Phillippi, Amphipolis, Apollonia, Thessalonica, Brea, Athens and Corinth. It came nowhere near Illyricum. On the occasion of the later visit, it was natural that he should refer to Illyricum in the letter to the Romans, since he had been near there recently.
The Origin of the Organic World – Part One