Ancient physician Galen (131 - 201 A.D.) developed the principle of humors, linking body type with health and personality. For the next 1,400 years, physicians would trust in Galen's principles for better or worse, often using them as the basis for purgatives and bloodletting. In the 16th century, however, one physician would break ranks with the Galenic school to propose his own somewhat strange idea known as the Doctrine of Signatures. Paracelsus (1493 - 1541 A.D.) would reject humors and instead argue that botanicals bear an uncanny resemblance to the body parts, or causes of the ailments, they could cure.
Herbs in Medieval Europe
The progress of science and the understanding of plants nearly collapsed with the fall of the Roman Empire. The early Middle Ages saw a return to the ritual and superstition that surrounded herbs, as the learning of the ancients was preserved mostly in monasteries and the Arabic cultures. Some herbs were positively reviled in Medieval Europe. A common Medieval belief held that scorpions bred beneath Basil pots, and inhaling the Basil's scent would drive a scorpion into the brain.
The Renaissance
As Europe emerged from the Middle Ages, trade with other civilizations increased, and so did the knowledge of medicinal herbs. In fact, the "discovery" of the New World was fueled by a quest for herbs and spices — Columbus was seeking a quicker, cheaper route to India in 1492. During the Renaissance, nobles of Europe aspired to assemble all human knowledge in their private libraries, and all useful botanicals in their gardens.