A subway construction project in Thessaloniki, Greece has unearthed an 1,800-year-old road built by the Romans and an even older road beneath it.

The 70-metre section of Roman road was paved in marble, with some of the stone blocks worn down by the wheels of horse-drawn carts. Archeologists believe it was the city's main travel artery nearly 2,000 years ago.

Beneath the Roman road is an even older pathway built by the Greeks 500 years earlier, according to archaeologist Viki Tzanakouli.

"We have found roads on top of each other, revealing the city's history over the centuries," Tzanakouli said.

"The ancient road and side roads perpendicular to it appear to closely follow modern roads in the city today."  

The excavation site was shown publicly on Monday, with the city also announcing details of a plan to permanently display the ancient road when the subway opens in 2016.

The Roman road was found seven metres below ground in the centre of the city. Some of the large stones were etched with children’s board games, while the bases of marble columns ran alongside the road.

Ancient tools and lamps were also discovered by the archeologists at the dig site.

Work began on Thessaloniki's new subway system in 2006, but there have been delays because of Greece’s financial problems and the need to work carefully in a part of the world where ancient artifacts might turn up at any time.

In 2008, staff working on the Thessaloniki subway discovered more than 1,000 graves, some containing jewelry, coins and other artifacts.

The city's subway system is due to begin operating with 13 stations in 2016, with 10 more stations to be added later.