Circular Structure Interior

View of the interior of the "circular structure" that is located in the center of the agora/forum.  Note all of the clay pipes in the center of the image along with what looks like a (partial?) hemispherical domed roof(?).  Given all the clay pipes, it seems like this structure was filled with water.  I wonder if it might have been a place to store live fish that would have been sold in the market place?

This structure is 45 ft. [13.5 m.] in diameter.

However, some suggest that it may have been a temple to the patron deity of merchants — Hermes, but this seems doubtful in light of all the clay pipes.