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").
Constructed as a hypostyle hall with a quadrangular plan to produce four rows of twelve cross-shaped pillars per row, this structure partitions the interior into five long aisles and thirteen courtyards (similar to a cathedral, hence its nicknames).