Its plan is a rotunda resting on a Decagonal lower chamber, each side of which is recessed and arched by great blocks of limestone set as the Etruscans set the roofs of their tombs.
"Cathedral Cities of Italy"
William Wiehe Collins
The upper story is also Decagonal, and is reached by a flight of modern stone steps.
"Saunterings"
Charles Dudley Warner Last Updated: February 22, 2009