four large arches, those of the three niches, and that of the entrance namely, which form the Cross of the Church. From that point upwards commences the Cupola itself, which springs from a basement of travertine, with a platform six palms broad, forming a wall or passage around the building. That basement presents a circle in the manner of a well, the thickness thereof being thirty-three palms eleven inches, the height to the upper cornice eleven palms ten inches; the upper cornice is about eight palms, and it projects about six palms and a half. Through this basement there are made four entrances by which the ascent to the Cupola is commenced, and these are placed above the arches of the Tribunes, the thickness of the basement being divided into three parts. The innermost division measures fifteen palms, the outermost eleven palms, and that in the middle seven palms eleven inches, which make the thirty-three palms eleven inches before mentioned.
The middle portion of the basement is unencumbered and serves as a passage, its height is equal to twice its breadth, it has a coved ceiling, and in the line of the four entrances it has eight doors, each joined by four steps, one leads to the level of the cornice of the first basement, which is six and a half palms broad, another conducts to the inner cornice, eight and three quarters palms broad, which encircles the Cupola.
These doors give commodious access to the inside as well as outside of the edifice. The distance from one to another forms the segment of a circle of two hundred and one palms, and these being four, the entire circle is one of eight hundred and four palms. This basement, whereon repose the columns and pilasters, and which forms the interior frieze of the windows, is fourteen palms one inch high, and on the outside there is a slight cornice above and below, which does not project more than ten inches, and is entirely of travertine.
In the thickness of the third part, above that of the interior, and which we have described as being fifteen palms broad, there is a staircase four and a quarter palms broad in each quarter of the circle; it has two branches, the one turning one way and the other in the opposite direction; these staircases lead to the level of the columns, above which, and immediately over the centre of the basement, there rise eighteen[1] large piers entirely of travertine, each adorned
- ↑ Since the drum is octagonal, there cannot be more than sixteen piers. Ed. Flor., 1832-8.
