Which book is considered one of the most influential in architectural history, celebrated for its purity and simplicity of classical architecture?

The book that is celebrated for its purity and simplicity in classical architecture is indeed the "Ten Books of Architecture" by Vitruvius, which is often referenced in discussions about architecture. This work holds significant influence because it establishes fundamental principles of architecture, emphasizing the relationship between structure, utility, and beauty. Vitruvius's emphasis on proportion, symmetry, and harmony has shaped architectural theory and practice throughout history.

The references to the other choices may cause confusion, as they don't correspond to significant texts in the realm of architectural theory. For instance, there are works like Palladio's "Four Books of Architecture," which also have considerable impact, focusing on classical design and the application of Vitruvian principles, but the clear intent of the question indicates the book associated specifically with classical architecture's foundational principles is the "Ten Books of Architecture" by Vitruvius. This foundational work is key in understanding the evolution of architectural thought.