1. History and the Student
2. Vitruvius, De Architectura (Ten Books on Architecture), ed and trans by Frank Granger (Cambridge: Harvard, 1941) vol I, took 1, chapter 1, p 5.
3. Paul Frankl, Principles of Architectural History, ed and trans by James F O'Gorman (Cambridge: MIT Press, 1968), p 11. This book appeared originally in 1913, dedicated to Heinrich Wölfflin. Sifgried Gidion, in Space, Time and Architecture, also paid eloquent tribute to his teacher: “As an art historian I am a disciple of Heinrich Wölfflin.”.