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A stoa (//; plural, stoas, stoai, or stoae //), in ancient Greek architecture, is a covered walkway or portico, commonly for public use. Early stoas were open at the entrance with columns, usually of the Doric order, lining the side of the building; they created a safe, enveloping, protective atmosphere.
Later examples were built as two stories, with a roof supporting the inner colonnades where shops or sometimes offices were located. They followed Ionic architecture. These buildings were open to the public; merchants could sell their goods, artists could display their artwork, and religious gatherings could take place. Stoas usually surrounded the marketplaces or agora of large cities and were used as a framing device. 
The name of the Stoic school of philosophy derives from "stoa".