Acts 17:6,8 mention the “rulers of the city” of Thessalonica, who beat and imprisoned Paul and Silas. Luke, the inspired writer of Acts, is a most careful historian. Different cities/districts used specific words to designate their rulers. Here Luke uses the word “politarch” (πολιτάρχης) which was a “very rare title for magistrates” (see Schaff below). Was Luke correct or was he mistaken?
Last month in London I was able to photograph a very important inscription, the Politarch Inscription of Thessalonica, removed from a Roman gateway of the city.

Inscription from Thessalonica using the word “politarchs” to designate rulers, as found in Acts 17:6,8. Photo ©Leon Mauldin. British Museum.
Church historian Philip Schaff, in a section entitled “The Acts and Secular History,” wrote:
The “politarchs” of Thessalonica, 17:6, 8 (Greek text: τοὺς πολιτάρχας, i.e., τοὺς ἄρχοντας τῶν πολιτῶν, praefectos civitatis, the rulers of the city).
This was a very rare title for magistrates, and might easily be confounded with the more usual designation “poliarchs.” But Luke’s accuracy has been confirmed by an inscription still legible on an archway in Thessalonica, giving the names of seven “politarchs” who governed before the visit of Paul.
The Thessalonian inscription in Greek letters is given by Boeckh. Leake, and Howson (in Conybeare and Howson’s Life and Letters of St. Paul, ch. IX., large Lond. ed., I. 860). Three of the names are identical, with those of Paul’s friends in that region-Sopater of Beraea (Acts 20:4), Gaius of Macedonia (19:29), and Secundus of Thessalonica (20:4). I will only give the first line:
ΠΟΛΕΙΤΑΡΧΟΥΝΤΩΝ ΣΩΣΙΠΑΤΡΟΥ ΤΟΥ ΚΛΕΟ. (Schaff, P., & Schaff, D. S. (1910). History of the Christian church (Vol. 1, p. 735). New York: Charles Scribner’s Sons.
Schaff earlier in that section mentioned the significance and importance of such artifacts as pertains to the book of Acts:
Bishop Lightfoot asserts that no ancient work [as that of Acts, L.M.] affords so many tests of veracity, because no other has such numerous points of contact in all directions with contemporary history, politics, and typography, whether Jewish or Greek or Roman. The description of persons introduced in the Acts such as Gamaliel, Herod, Agrippa I., Bernice, Felix, Festus, Gallio, agrees as far as it goes entirely with what we know from contemporary sources. The allusions to countries, cities, islands, in Syria, Asia Minor, Greece, and Italy are without exception correct and reveal an experienced traveler. Ibid.732)
In other words, time and time again, Luke has been proven to be right! You can trust the Bible!
The British Museum Curator’s comments are interesting:
This large stone was built into a wall at the Vardar Gate of Thessalonica and was removed in 1877. The stone has been assumed to name city officials of the era. The inscription is important to New Testament scholars because it is one of the few stones that attests the existence of the office of politarch, mentioned in the Bible (Acts 17:6 and 8) and in only a few other literary sources. It is also curious because it mentions the mothers as well as the fathers of two of the politarchs. How the number of politarchs in this inscription should be counted varies among the modern editions; the translation here presents the usual interpretation of the inscription (see vom Brocke). (http://www.britishmuseum.org/research/collection_online/collection_object_details.aspx?objectId=398975&partId=1)
I should mention that this inscription is not regularly on display. It took three days to get an appointment to go into the room where is it housed, but it was worth it!
Click images for larger view.