“In Tivoli, fixteen miles diflant from Rome , upon the fall of the river Aniene, now called Teverone , the following round temple is to be seen, which the inhabitants of these places say was the room of the Sibilla Tiburtina: which opinion is without any foundation. However I believe (for the reafons beforementioned) that it was a temple dedicated to the goddess Vesta.
This temple is of the Corinthian order. The intercolumniations are of two diameters. Its pavement is railed from the ground the third part of the length of the columns. The bafes have no plinth, that the place to walk in under the portico might be more free and ample. The columns are as long cxactly as ilic cell is broad, and they incline inwardly towards the wall of the cell ; fo that the fhaft of the column above falls perpendicularly upon the fhaft of the column below in the inward part… (Palladio)