Roman Inscriptions

These stones have Latin writing on them instead of the usual Greek in the region. This is because Philippi was a Roman colony. As Luke records travels of the Apostles, including Paul, in Acts:

...from there to Philippi, which is a leading city of the district of Macedonia and a Roman colony. We remained in this city for some days. chapter 16:12

To continue with Paul through Philippi, go to Lydia's baptism.

Why are the Latin inscribed rocks significant for understanding the world of Paul?

Philippi was a Roman colony and Paul uses the imagery of citizenship to talk about life in Christ:

Only live your life as worthy (citizens) of the gospel of Christ, so that, whether I come and see you or am absent and hear about you, I will know that you are standing firm in one spirit, striving side by side with one mind for the faith of the gospel. (Philippians, chapter 1:27; my translation based on the NRSV)

But our citizenship (colony) is in heaven, and it is from there that we are expecting a Savior, the Lord Jesus Christ. (Chapter 3:21)

The words in parenthesis show the meaning of the underlying Greek.

What is a citizen?

The citizen of Paul's day did not merely mean resident but person with rights, including, for example, the right to a trial. In the later half of Acts, the impetus for action is getting citizen Paul his fair trial. Citizens also had the right to vote, to marry, and make contracts. They had the responsibility to pay taxes and serve in the military.

The most essential features of citizenship are that it came with right and that it was exclusive. Not everyone was granted citizenship.  It is estimated that only 15% of the population were actually citizens.

How is Paul remixing the culture?

Paul makes two striking points about citizenship. First, he declares the ultimate citizenship of someone is not in the Roman Empire, but in Christ Jesus. For colonists granted citizenship in the Roman Empire and often former veterans, this would be a bold statement. The state which you served for twenty years and now gives you power through your rights...that state is not your ultimate loyalty!

The second claim is that Paul claims our citizenship in God's kingdom is based neither on birth nor our own military victories. It is all made possible by Christ.  That is unthinkable!

sources:
info on citizenship: http://www.dl.ket.org/latin1/mores/law/citizenship.htm  and http://www.legionxxiv.org/history/ 
info on citizenship: http://www.polyconomics.com/searchbase/03-12-99.html
info on greek words: Bauer, Walter. Greek‑English Lexicon of the New Testament and Other Early Christian Literature. ed. by Danker, Arndt, Gingrich, 3rd ed. Chicago: University of Chicago Press, 2000, available through Bible Works.