Romans 15:19
Writing to the Christians in Rome, Paul both lays out his credentials and explains why he has not yet visited the Church in the greatest city in the world. He explains that his desire to break new ground with the gospel message has taken him "...from Jerusalem all the way around to Illyricum,...".
Geographically, Jerusalem and Illyricum represent the eastern and western limits of Paul's ministry in Palestine, Syria, Asia Minor, Macedonia and Acahaia. See below.
Apparently Paul wanted to cover this territory thoroughly before crossing the Adriatic to continue his ministry in mainland Italy.
Both Illyricum and Dalmatia (2 Timothy 4:10) refer to a mountainous region on the eastern shore of the Adriatic Sea. The name of the region did not remain static throughout antiquity. I have found it difficult to come to clear understanding of the exact relationship between the Roman provinces of Illyricum and Dalmatia, and the timing of name changes, but for the purposes of following Paul, the western terminus of the via Egnatia at Dyracchium (Durrës, Albania), is clearly significant.
No doubt, Paul traversed large sections of the via Egnatia, probably for the first time between Neapolis and Philippi, and then as part of his journey further west to Thessaloniki. We have no Biblical narrative of Paul's presence in Illyricum. (Although, it is worth pondering to what extent the controversy about the location of Paul's shipwreck (Acts 28) has any bearing on ehtis question.
For the purposes of following Paul's claim to have preached the gospel "all the way around to Illyricum", the western end of the via Egnatia works for me.
The traveler with time and resources to explore Illyricum more widely, might also consider visiting Salona, near Spilt, Croatia.
Click here for a Google Earth view of 'Illyricum'.
I have not yet been able to visit the ruins of Salona, the ancient capital of Illryicum, but one day I hope to be able to use these coordinates to do so.
The amphitheatre dates from the second century, so well after Paul's time, but would still be worth seeing.