This lecture covers the foundational concepts of geometry, focusing on Euclidean propositions and the evolution of symmetry from ancient commensurability to modern symmetry. It explores the construction of geometric figures, the power of a point relative to a circle, and the concept of radical axis. The instructor delves into the historical context of geometry, including the works of Euclid and Vitruvius, and their impact on architectural principles. The lecture also discusses the significance of the De Architectura in understanding geometric constructions and the practical applications of geometry in architecture.