This document provides a historical overview of the city of Thessaloniki, Greece. It discusses that Thessaloniki was founded in 315 BC and has a history spanning over 2,300 years. As the second largest city of the Byzantine Empire, it contains many notable Byzantine monuments from that era. The document describes some of the most prominent historical sites from Thessaloniki's Roman and Byzantine periods, including the Rotunda, Arch of Galerius, and various churches. It outlines how Thessaloniki became an important center of Christianity and the spread of the faith in the region.