 Riehl supervised Frankl's doctoral dissertation on fifteenth-century glass painting in southern Germany.After the completion of his dissertation in 1910, Frankl worked as Wölfflin's assistant and wrote his "Habilitationsschrift", which offered a systematic definition of the formal principles of architecture from the Renaissance onwards.Frankl was heavily influenced by Wölfflin's understanding of architectural development, but did not adhere to Wölfflin's views on formalism.