The appearance of the south side of the Agora was radically changed during the 2nd century B.C. with the construction of several new buildings. This South Square, as it is called, was made up of two long stoas with a third building linking them (Fig. 38). Of the Classical buildings, the Aiakeion and Southwest Fountain House were incorporated, South Stoa I was demolished, and the Southeast Fountain House and Mint were left out. The new square can best be understood from the so-called East Building, just north of the Church of the Holy Apostles.
First to be built was the Middle Stoa, which ran east–west across the old square, dividing it into two unequal halves and obscuring one of the original boundary stones at its western end. At just under 150 meters long, it is the largest building in the Agora, with colonnades at both north and south as well as down the middle. Traces of a narrow parapet that ran between some of the columns can be made out on individual drums. The original steps and three columns remain in situ at its eastern end; to the west, only the heavy foundations of reddish conglomerate survive. Except for its size the stoa is a relatively modest building, made of limestone, with a terracotta roof (Fig. 39). It was built between ca. 180 and 140 B.C.