Abstract: An auditorium has a domed roof formed by a first part spherical portion covering, without intermediate support, most of an amphitheatre accommodating an audience, and a second part spherical portion covering a stage adjacent the amphitheatre, the first portion being supported only at its periphery, and the second portion consisting of segmental leaves which can open about a common pivot supported by the first portion to uncover the stage, the common pivot being at a vertical axis of the second portion of the roof and above the amphitheatre and the vertical axis of the first portion being above the stage. Wall panels behind the stage can be moved apart to open the rear of the stage to the exterior.