Illyricum

Illyricum was the Roman province occupying the eastern Adriatic coast and its hinterland — roughly the territory of modern Croatia, Bosnia, and western Serbia. It lay northwest of Macedonia and formed the northwestern boundary of Paul's missionary activity in the eastern Mediterranean. In Romans 15:19 Paul states that he has fully preached the gospel of Christ "from Jerusalem and round about unto Illyricum" — indicating that by the time of writing he considered his work in the east complete and was ready to move westward to Spain via Rome.

The reference implies Paul had reached Illyricum, though Acts does not record a specific mission there. Most scholars understand the visit to have occurred during the period described in Acts 20:2, when Paul traveled through Macedonia before returning to Greece. Illyricum represents the westernmost point of Paul's confirmed missionary geography in the eastern empire, and the verse in Romans is one of the few explicit geographic claims Paul makes about the extent of his completed ministry. The province was later called Dalmatia; 2 Timothy 4:10 mentions Titus going to Dalmatia, which may overlap with this region.