This chapter examines two of the primary cognitive artifacts of Euclidean geometry, namely the lettered diagram and a professional discourse containing the linguistic formulae that served as scaffolding for the emergence of epistemic values concerning the necessity of inference steps and the generality of proved theorems. It focuses on the structure and function of the diagram. The chapter looks at how the combination of both cognitive artifacts serves as the scaffolding for the necessity and generality of Euclidean reasonings. It argues that specificity of the professional language of geometry is not only limited to the latitude or the cultural circle, since it differs considerably in comparison to other professional discourses such as the anatomical one, which was also developed in ancient Greece. The chapter summarizes the inquiry and considers how it may be informative for further studies on the geometric cognition of contemporary individuals.