NOVA's bath, like hundreds of Roman baths before it, is crowned with a vaulted roof, another Roman innovation. Before them, the Greeks built temples and other large buildings by supporting large flat roofs with many columns.
The Romans improved on the design, building curved roofs with a keystone dropped into the top of the vault. The downward thrust of the keystone pushed the sections outward, creating a pressure that held the entire roof together. The curved roof makes the columns unnecessary, freeing the interior space of its weighty columns.
NOVA's vaulted roof is built of bricks. A tense moment during the bath's construction comes when the wood form underneath the vault is removed. If the vaulted roof isn't built correctly, it would cave in when the wood forms are removed. Lucky for all, the roof holds.