After the fall of the kingdom of Macedon in 168 BC, Thessalonica became a city of the Roman Republic. It grew to be an important trade-hub located on the Via Egnatia, a Roman road that connected Byzantium (later Constantinople), with Dyrrhachium (now Durrës in Albania), facilitating trade between Europe and Asia. The city became the capital of one of the four Roman districts of Macedonia. It kept its privileges but was ruled by a praetor and had a Roman garrison. For a short time in the 1st century BC, all the Greek provinces came under Thessalonica. Due to the city’s key commercial importance, a spacious harbour was built by the Romans, the famous Burrow Harbour that accommodated the city’s trade up to the eighteenth century; later, with the help of silt deposits from the river Axios, it was reclaimed as land and the port built beyond it. Remnants of the old harbour’s docks can be found nowadays under Odos Frangon Street, near the Catholic Church.
Thessaloniki’s acropolis, located in the northern hills, was built in 55 BC after Thracian raids in the city’s outskirts, for security reasons.
It had a Jewish colony, established during the first century, and was an early centre of Christianity. On his second missionary journey, Paul of Tarsus preached in the city’s synagogue, the chief synagogue of the Jews in that part of Thessaloniki, and laid the foundations of a church. Opposition against him from the Jews drove him from the city, and he fled to Veroia. Paul wrote two of his epistles to the Christian community at Thessalonica, the First Epistle to the Thessalonians and the Second Epistle to the Thessalonians.
Thessaloníki acquired a patron saint, St. Demetrius, in 306. He is credited with a number of miracles that saved the city. He was the Roman Proconsul of Greece under the anti-Christian emperor Maximian and was martyred at a Roman prison, where today lays the Church of St. Demetrius, first built by the Roman sub-prefect of Illyricum Leontios in 463.
Other important remains from this period include the Arch and Tomb of Galerius, located near the center of the modern city.