Le Castellum Divisorium

I had a little pocket map of the major sights in Nîmes that I was using to guide myself around. One marking was the Castellum which is where the aqueduct comes into the city and the water is distributed. From the map it looked like it would be very impressive. I imagined something rivaling a modern day pumping station or something like that. I went to the location on the map and had difficulty finding the thing. It looked like it took up a whole block, so how could I be missing it. After walking around a while I finally figured it out. The Castellum was a little stone thing that was maybe 10ft in diameter and had one small pipe coming in from the aqueduct and a few pipes going out. I was underwhelmed. Even the pictures on these websites make the thing look like it was some huge technological marvel.
http://www.arch.mcgill.ca/prof/sijpkes/abc-structures-2005/Lectures-2005/lecture-5/nimes_castellum.html
http://monuments.nimes.fr/castellum/j_castellum.htm
I guess in the context of being 2000 years old it is impressive, but if they could build the Pont du Gard, I would hope the Castellum would be pretty easy to fabricate.