Around 1,000 graves, some of them containing jewels, coins and artworks, were discovered to the east of the city center at the site of a former cemetery.
Most of the graves date back from the first century B.C. to the fifth century A.D. Thessaloniki was founded in 315 B.C and is believed to have been named after the sister of Alexander the Great by King Cassander of Macedon.
A separate group of 94 graves was also discovered near the railway station at the site of another ancient cemetery in Thessaloniki. The graves range from plain coffins to five-room marble mausoleums.
Work on the city's subway system started in 2006 and city officials say the first 13 stations are to be completed by 2012.
Similar tombs from the same era were discovered in Athens during excavations in the 1990s prior to the construction of the city's subway station, but were destroyed by workers. Parts of them are now on display in several metro stations.