Walking down the nave, you come to the heart of the co-cathedral: the high altar, designed in the neoclassical style by the Sienese architect Agostino Fantastici; one of his drawings for it, made in 1828, still survives. The altar presents an original design: in the center is the façade of an ancient Greek or Roman temple, recalling the sacrificial dimension of the Mass. While in the liturgy of . . .