stoa (stōˈə) [key], in ancient Greek architecture, an extended, roofed colonnade on a street or square. Early examples consisted of a simple open-fronted shed or porch with a roof sloping from the back wall to the row of columns along the front. Later stoas were often immense, running to two stories, each with a colonnade of a different order and having a ridged roof supported on internal colonnades; rows of shops or offices lined the back wall, which was sometimes decorated with paintings. Such stoas surrounded the agora or marketplace of every large city and were used for public meetings. The Stoa Poecile on the north side of the agora of Athens was the favorite meeting place of the philosopher Zeno of Citium; hence his followers are called Stoics and his system Stoicism.