 "Die Entwicklungsphasen" proposes four major categories of art history analysis - spatial composition, treatment of mass and surface, treatment of optical effects, and the relation of design to social function - that Frankl continued to draw upon in his later work.Frankl held an assistant professorship at the Ludwig Maximilian University of Munich from 1920 to 1921, after which he became full professor at Halle University.It was here that Frankl initiated his lifelong interest in medieval architecture.