This book is made up of the scripts of a series of television programmes given in the spring of 1969. Writing for television is fundamentally different from writing a book, not only in style and presentation, but in the whole approach to the subject. People who settle down to an evening’s viewing expect to be entertained. If they are bored they switch off. They are entertained as much by what they see as by what they hear. Their attention must be held by a carefully contrived series of images, and often the sequence of images controls the sequence of ideas. The choice of illustration is itself determined by certain material accidents. Some places are inaccessible, some buildings defy the camera, some locations are too noisy for sound recording. All these considerations have to be in the writer’s mind from the beginning, and modify or direct his line of thought. But more important still, every subject must be simplified if it is to be presented in under an hour. Only a few outstanding buildings or works of art can be used as evidence, only a few great men can be named, and what is said about them must usually be said without qualification.