Carl Boetticher, Gottfried Semper, and Heinrich Woelfflin: a sketch of various investigations on the nature of "Tectonic" in nineteenth-century architectural theory. The essay sketches the shifting understanding of the tectonic in the architectural theories of Carl Boetticher, Gottfried Semper, and Heinrich Woelfflin. The essay argues that the axiomatic definition of the tectonic as "Poetics of Construction", as it has been advocated in recent decades, is focusing too one-sidedly on architecture's tangible materiality and undermines the capability of architecture to contain representational values and to hold civilizing meaning.