The original portico ceiling was however most unusual, being made of bronze, of which all the visible surfaces were presumably sculpted. This bronze ceiling had to span across the gaps between the rows of support columns, up to about twelve metres apart, perhaps in order to avoid putting too much weight on the stone roof slabs. It is therefore clear that the Romans were aware of the structural principle that a tube makes a strong and stable beam, a principle often employed in engineering. The Pantheon still stands in the centre of Rome, and while its outside is dull the interior is one of the most breathtaking sights in that remarkable city. Unfortunately, however, the bronze portico ceiling and its beams cannot be inspected today.
Few records remain of the ceiling's former splendour.