In the first century BC, nearly two thousand years before the invention of the microscope, the Roman scholar Marcus Terentius Varro made a remarkable observation about the cause of disease. Writing in his agricultural treatise De Re Rustica around 37 BC, Varro advised landowners to avoid building homes near swamps. His reason was unusual for the time:
There are bred certain minute creatures which cannot be seen by the eyes, which float in the air and enter the body through the mouth and nose and there cause serious diseases.
The statement sounds astonishingly similar to the principles of germ theory. Varro described invisible living organisms too small to be seen, entering the human body and causing illness. Although he lacked any means of observing microorganisms and had no scientific evidence to support his claim, his words represent one of the closest approaches to germ theory found in the ancient world.
Varro was one of the most learned men of the Roman Republic. Born in 116 BC, he wrote on subjects ranging from history and literature to language, philosophy, and agriculture. Of the hundreds of works he produced, only a small portion survives today, including De Re Rustica, a practical guide to farming and estate management.
It was in this work, and not in a medical treatise, that Varro made his famous observation. While discussing the ideal location for a country estate, he warned readers against settling near marshes. Such places, he argued, generated invisible creatures that could enter the body through the nose and mouth and cause disease. At a time when illness was commonly explained through supernatural causes or imbalances within the body, this was an extraordinary suggestion.
Varro was attempting to explain a real phenomenon. Throughout the ancient Mediterranean world, people had long noticed that those who lived near marshes often became sick. Today we know that marshlands provide ideal breeding grounds for mosquitoes, which can transmit malaria and other diseases. The ancient Romans, however, knew nothing of mosquitoes as disease vectors. Most explanations focused on unhealthy vapours or foul-smelling air rising from stagnant water.
Varro, instead of merely blaming bad air, imagined that swamps produced tiny living creatures that drifted through the atmosphere and entered the body. While his explanation was not entirely correct, it brought him surprisingly close to the truth.
Varro did not invent the concept out of thin air. Greek philosophers had long speculated about invisible particles moving through the world. The atomists, such as Democritus, proposed that all matter consisted of tiny indivisible units. The Roman poet Lucretius, writing in the first century BC, suggested that invisible “seeds” or particles could spread disease. Varro went a step further, by proposing that these invisible particles were living creatures. In effect, he imagined microscopic living things capable of causing disease.
Although it would be a stretch to view Varro as a forgotten discoverer of germs, several elements of his description are remarkably accurate. He proposed that disease could be caused by living organisms too small to be seen with the naked eye, which enter the body from the environment. For a writer working nearly 2,000 years before the microscope, that's an astonishing intellectual leap.
Despite its originality, Varro's insight had little impact on the history of medicine. Ancient and medieval medical thought was dominated by the theory of the four humors, which held that illness resulted from imbalances in bodily fluids. This framework, developed by Greek physicians and later expanded by Galen, remained influential for well over a thousand years. Besides, Because Varro's observation appeared in a farming manual rather than a medical work, and thereby attracted little attention from physicians.
It was not until the 19th century, when scientists such as Louis Pasteur and Robert Koch demonstrated the role of microorganisms in disease, that Varro's ancient speculation became established science.
References:
# Varro. De Re Rustica
# Certain Minute Creatures. University of Queensland
# Marcus Terentius Varro. Wikipedia
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