It was built as a kind of hypostyle hall on a quadrangular plan to obtain four rows of twelve cruciform pillars per row which divide the interior space into five long naves and thirteen courtyards (just as if it were a cathedral, hence its local nicknames of "the Water Cathedral" or the "Cathedral of Bacoli").
Built as a hypostyle hall on a quadrangular plan to create four rows of twelve cross-shaped pillars per row, which divides the interior space into five long aisles and thirteen courtyards (just like a cathedral, thus earning it local nicknames such as "the Water Cathedral" or "Cathedral of Bacoli").