The Middle Ages are often seen as a shadowy period of limited medical knowledge and great superstition. But many ideas from the classical medicine of the ancient Greeks and Romans survived into the medieval period relatively intact. Medical knowledge also arrived in Europe from the Arab world over the centuries, and doctors were familiar with the medicinal properties of some plants. However, treatments and cures were often as much to do with magic and superstition as they were to do with real medicine.
Doctors were very much guided by astrology in the Middle Ages. The Church, which influenced so much of medieval life, strongly disapproved of astrology, but found it difficult to stamp out. During the worst period of the Black Death, astrological charts became even more important for doctors. As the illness reached a noticeable crisis point, after which a patient either recovered or died, the time of recovery and the position of the stars and planets were seen as very significant. Even Guy de Chauliac, physician to three popes in succession, and author of the leading work on medieval surgery, was a firm believer in astrology. For operations, he would use recognized anesthetic potions, but also recommended bleeding and other procedures based on the position of the planets. Illnesses were also determined to be serious or not depending on whether they were under the sun’s or the moon’s influence. You can learn more about The Heretic's Tomb and the historical background to the novel on my website.