In Greek architecture, a freestanding colonnade or covered walkway; also, a long open building with its roof supported by one or more rows of columns parallel to its rear wall.
Stoas lined marketplaces and sanctuaries and formed places of business and public promenades. Rooms might back onto the colonnade, and a second story was sometimes added. The Stoa of Attalus in Athens (2nd century BC), a large, elaborate, two-story building with a row of shops at the rear, was a prime example.