THE ROOTS OF spine biomechanics reside in the Antiquity and the Medieval and Renaissance periods. A review of historical treatises reveals detailed information regarding this often historically neglected discipline. Ancient medical, philosophical, and physical documents were reviewed, as they pertained to the historical foundation of spine biomechanics. These included medical case reports and observations of nature and motion by ancient philosophers and scientists. These documents heavily influenced the portion of the scientific literature that we now regard as "spine biomechanics" up through the Renaissance. The focus of Part I of this two-part series is placed on the ancient and medieval biomechanics-related literature and on associated literature that influenced the development of the field of modern spine biomechanics.