An ancient portico -- a long, open structure often housing shops -- unearthed in northern Greece has been dated at 2,700 years old, Canadian archaeologists say.

In ancient Greece, porticos -- stoa in Greek -- delineated public squares from the city center, the agora.

"Porticos are well known from the Hellenistic period, from the 3rd to 1st century B.C., but earlier examples are extremely rare, University of Montreal archaeologist Jacques Perreault said. "The one from Argilos is the oldest example to date from northern Greece and is truly unique."

Located on the edge of the Aegean Sea, the ancient city of Argilos was the first Greek colony established in this area and at its peak in the 5th century B.C. was one of the richest cities in the region, the researchers said.

Digs conducted this year have uncovered around 130 feet of the portico's length, they said, containing seven rooms each measuring around 15 feet wide by 22 feet deep.

"The construction techniques and the stones used are different for one room to another, hinting that several masons were used for each room," Perreault said. "This indicates that the shop owners themselves were probably responsible for building the rooms, that 'private enterprise' and not the city was the source of this stoa."