Rotunda set within a Proscenium Arch

Franz Rapp considers this drawing "apparently the work of Francesco, who designed the Vienna Opera House of 1700".
The attribution of drawings by the Bibiena family and their circle is a famously difficult matter, and this drawing presents a notable case of how scholarly opinion may vary, as noted by Donald Oenslager (Oenslager 1985, 64). Janos Scholz (1949) attributed it to Giuseppe Galli Bibiena, but Franz Rapp (1951), in a review of Scholz's book, gave it to Francesco, an attribution supported by Richard Wunder (1963) and (with some hesitation) by Diane Kelder (1968). Muraro and Polvedo (1970) return it to Giuseppe, an attribution also endorsed by Oenslager. Kelder later (2000, 115) returned to the earlier attribution as well, discussing the drawing as "attributed to Giuseppe." A smaller replica of this drawing is at the Tiroler Landesmuseum at Innsbruck (inv. A 3), attributed to Giuseppe.