This small temple, probably honoring Demeter, was converted to a small church/chapel in Byzantine times. The agora was already covered and you can see where they replaced the four columns with walls and the side facing us would have been the apse. In the foreground you can see a square structure, that was the altar for sacrifices when the agora was functioning. The altar is open to the ground so sacrifices would have had the blood draining into the ground, which is why it is assumed this temple honored Demeter.