Yet, it still shows the remains of a dome roof/ceiling. Most removed over the years for use in other structures, but the pillars remaing show the schematic. It's the domes.
Like the dome st Esptein's temple, the dome and the bathhouse in Aleppo. They showcase the keystone, which is the secret of how the dome stands. The dome is emblematic of the sky. The carvings on the pillar shows who they worship who holds up the sky.
Look at the dome in Newgrange and the spirals carved outside.