Some say the monastics of the Middle Ages merely kept good records of the classical era, preserved them, copied them, and made use of them. Others say they developed many skills and a great deal of information themselves through trial and error. What cannot be doubted, though, is that monks and nuns of medieval times had records, gardens and medicines for the practice of herbalism. Indeed, they were the practicing masters of it, particularly the Benedictines, and they held and built this treasure of knowledge for over a millennium, with some continuing to do so to this day.
Ancient Rome used herbs as part of its medical system. Indeed, the Roman Army took seeds with them along the way so they could plant and use them when they dug in at a particular location. The system itself came mainly from Greek discoveries, particularly Hippocrates and his followers, and it is well recorded that the Hippocratic humeral system was used by Ancient Rome. This system held that an excess or deficiency of any of four bodily fluids in a person, called humours, had a direct effect on their health and attitude. Herbs were among the things that they thought could restore balance to the humours. While the system was flawed in its foundational assumptions, the trial and error involved in it led to discovering many herbs and plants that helped the body to heal itself.