Did Galen written any books about his medical ideas?

Yes, Galen wrote extensively about his medical ideas, producing numerous texts that greatly influenced the field of medicine. His most notable works include "On the Use of Parts," where he discusses anatomy and physiology, and "On the Diagnosis and Cure of Diseases," which outlines his clinical practices. Galen's writings synthesized earlier medical knowledge and introduced his own theories, particularly regarding the humoral system. His texts remained authoritative in medicine for many centuries.