The Silk Roads are an instructive reminder that human beings do not occupy isolated worlds but a shared and interdependent one that flourishes when they interact with one another. Interactions across vast distances, such as those which took place along these historic routes, have made an undeniable contribution to the enrichment of life and culture. Now, as in the past, increasing human interconnectedness and movement presents challenges but also opportunities in numerous fields including science, medicine and epidemiology, and greatly adds to the improvement and richness of our daily lives. The constant movement and mixing of populations along the Silk Roads had a profound impact on the history and civilizations of the peoples of Eurasia and indeed of people worldwide, driving the development of knowledge, ideas, beliefs, culture and identities. Science, arts and literature, as well as knowhow, crafts and technologies were shared and disseminated into societies along the lengths of these routes.
However, wherever people, animals and goods have moved and brought enriching effects, undesirable phenomena such as disease have also been transmitted on a broad scale. Just as global movement and connectedness is not a new phenomenon, neither is the potential for, and the occurrence of, epidemics. Among the different kinds of parasites, bacteria and viruses, and their associated diseases, that were transmitted along the Silk Roads, plague was one of the most notable. Plague is a disease caused by the bacteria Yersinia pestis, commonly carried by fleas. Three pandemics of plague have occurred in human history: the best-known and perhaps largest was the second outbreak often referred to as the “Black Death”, which infected vast numbers of people across Eurasia, and killed somewhere between 75 and 200 million. The outbreak peaked between 1347 and 1351 CE, reaching the trade ports of Europe by 1346. A number of theories exist as to where the 14th century plague originated and how exactly it spread. One of the most often cited is that it was carried by infected rodents across the Silk Roads, reaching Europe along with infected merchants and travellers.
Societies were very limited in their ability to treat and prevent the spread of plague in the 14th century as there was no accurate knowledge available about the exact cause of the disease or of effective treatments. Indeed, fleeing remained one of the only effective preventative public health measures available to people at the time. Whilst the attempted cures for plague had very little effect, the Black Death did prompt Europe and other parts of the world to expand and refine public health measures, particularly in the subsequent decades and centuries as the disease continued to periodically return. Furthermore, some methods for preventing the spread of plague, such as making suspected vessels and travellers remain in isolation for 40 days before they were allowed to enter the city of Venice, are still practiced today, and it is from this practice that we derive the term “quarantine”.
The transmission of the Black Death, and the damage that it caused to societies in Asia and Europe, are undoubtedly examples of a disastrous catastrophe that trade, and interactions, helped exacerbate. However, an overall assessment of the outcomes of the exchanges along the Silk Roads reveals that despite some negative effects, these interactions have brought vast benefits and enriched human life and culture. In fact, the medical sciences have been one of the direct beneficiaries of these intercultural exchanges. During the medieval or “post-classical era” (500-1450 CE), scholars made large contributions to the fields of medicine, pharmacology and veterinary science thanks to the circulation of knowledge and ideas. The movement of people and knowledge across the Silk Roads facilitated the widespread translation of work from other parts of the world into Arabic, making a broad array of scholarship accessible to polymaths of the day. Their work synthesised and built on existing medical knowledge, such as that developed in Ancient Greece and Rome, and combined this with knowledge from other regions of the world such as China and the Indian subcontinent.
The example of the Black Death would be inspiring for dealing with challenges caused by the outbreak of epidemics in our contemporary world. Unlike in the 14th century, today we can identify new viruses, sequence their genome, and develop a reliable test for the disease in just a few weeks. It may be tempting in uncertain times, particularly now as the world is witnessing the rapid spread of COVID-19, to conclude that the only way to prevent challenges such as the spread of infectious diseases is to restrict movement and exchange, and somehow roll back globalization and the connectedness of different cultures and peoples. However, the spread of plague in a world without planes, trains and cruise ships, serves as a reminder that diseases can move rapidly even without such technologies.
Although we live in an age of intense globalization that seems unprecedented, human movement, exchange and interconnectedness are not recent phenomena. In fact, people have always moved from place to place and exchanged goods, skills and ideas across vast distances. The outbreak of the Black Death and its spread along the Silk Roads would be a timely reminder that one of the greatest defences against newly emerging challenges is the exchange and collective analysis of reliable knowledge and experience. Despite the tremendous speed of the circulation of people and goods around the world today, humans are well prepared and ready to face the challenges that may result from these interactions, largely thanks to collaborations and collective experiences and these will continue to play an important role in tackling and preventing the spread of diseases.
Historically, trade and movement have inevitably played a major role in the spread of infectious disease. In addition to diseases caused by bacteria, such as Plague, many viruses have been transmitted via movement along the Silk Roads. One notable example of a viral disease which has been prevalent throughout much of human history is smallpox. However, just as the disease itself travelled the Silk Roads, so too did a number of public health measures designed to combat it, including an early precursor to vaccinations, a practice known as “variolation”. Indeed, the first ever vaccines produced were used to protect people from catching smallpox, which, due to large scale international vaccination programmes in the 20th century, has since been successfully eradicated worldwide.
Smallpox is an infectious disease caused by the “Variola” virus characterised by the formation of small sores all over the body. The disease spreads via contact with an infected person or from a contaminated item such as clothing or bedding. Although the exact origins of smallpox are unknown, there is evidence of the disease having been present in Ancient Egypt from as early as the 3rd century BCE. It appears that trade played an early role in spreading smallpox and there is speculation amongst historians that traders from Egypt might have transmitted the disease to the Indian Subcontinent sometime in the 1st millennium BCE. Some of the earliest written descriptions of smallpox date from 4th century CE China and, as trade along the Silk Roads increased in the 6th century CE, the disease spread rapidly to Japan and the Korean Peninsula. Notably, smallpox broke out between 735 – 737 CE in Japan, where it is believed to have killed up to one-third of the population.
By the 7th century CE, as trade and travel along the Silk Roads increased, smallpox became “endemic” (outbreaks regularly reoccurring within a given population) in the Indian Subcontinent. Muslim expansion during this time spread smallpox into Northern Africa, Spain and Portugal. In the 9th century CE, the Persian physician Razi, an early proponent of experimental medicine and chief physician of Baghdad and Rey hospitals in the Abbasid Caliphate, produced one of the most definitive descriptions of smallpox and the first account differentiating it from other similar diseases such as measles and chickenpox. By the 10th century smallpox had spread throughout Anatolia, with another wave of increased activity along the Silk Roads in the 13th century CE causing the disease to become endemic in previously unaffected areas such as Central and Northern Europe. In the 15th century, Portuguese expeditions to the West Coast of Africa and the establishment of new trade routes introduced the disease to further previously unaffected areas.
Despite the fact that the movement of people and goods across vast distances has undoubtedly aided the spread of disease, the medical sciences have been one of the direct beneficiaries of the resulting intercultural exchanges. An excellent example of this is the development and transmission of “variolation”, a practice which was an early precursor to smallpox vaccination. There are early accounts of priests from the Indian Subcontinent travelling the Silk Roads popularising the practice of what they called “tika”, an early effort at inoculation (the introduction of a disease-causing agent in order to produce immunity to a specific disease). This involved taking matter from a smallpox patient’s sores and applying it to a small wound on an uninfected person, the idea being that the uninfected person would develop only a very mild case of the disease and, on recovery, become immune to catching a severe case in the future.
This practice may have developed independently in the Indian Subcontinent or, alternatively, practitioners might have learned it from Muslim physicians, who themselves came into contact with the practice via travel and trade with China. As early as the 1400s, medical healers in China had realized that those who survived smallpox did not catch the illness again and inferred that exposure to the illness protected a person from future instances of it. This observation gave rise to a second important public heath measure which was that those who had contracted the disease and survived were able to treat and care for new patients as they had incurred a natural immunity and were unlikely to become ill a second time. In order to transfer this immunity to new patients, Chinese doctors would grind smallpox scabs into a powder and insert it into a person’s nose with a long silver pipe. If only a very small amount of the virus was ingested that person would have a mild experience of the disease and be immunized for life. Similar practices, of “variolation”, were also documented in Africa in accounts from what is today Sudan. By the 16th century, this practice was a widespread public health measure enacted across many regions of the Silk Roads reaching as far west as Anatolia, having been introduced via descriptions from travellers and merchants.
Throughout history, as we have developed better knowledge of how diseases are transmitted, how they can be treated, and the relevant public health measures that prevent their spread, a major trend for many endemic diseases has been the gradual reduction in their impact over time. In the case of a number of viral diseases, these measures have included the development of vaccinations, which, as in the practice of variolation, have an historic precedent in medicine transmitted along the Silk Roads. In the 18th century, the English physician Edward Jenner built on the idea of variolation and made a major contribution to the development of the modern smallpox vaccine. He observed that those who had contracted cowpox, a similar but milder viral infection, rarely went on to catch smallpox later in life. It is from the disease cowpox, known in Latin as variola vaccina, that we derive the term “vaccine”. Coordinated international vaccination programmes throughout the 20th century led to the eradication of smallpox in 1980, and today outbreaks of the disease no longer occur anywhere in the world. The eradication of smallpox is a testament to the development of the medical sciences over a long period of time, building on and sharing pre-existing medical knowledge and coordinating public health initiatives. A natural precursor to this vaccination dates back many hundreds of years with its origins in the many exchanges in the medical sciences taking place along the Silk Roads.
The Development of Medical Botany and Pharmacology
Throughout history, trade and movement have inevitably played a major role in the spread of infectious diseases such as plague and smallpox. However, whilst disease undoubtedly travelled the Silk Roads, so too did knowledge surrounding the medicinal properties of various substances which might be used to mitigate its effects. In terms of the development of pharmacology, the interconnectedness the Silk Roads facilitated helped create an environment in which the synthesis of a broad array of medical traditions from across Eurasia could be carried out, and allowed for medicinal substances, predominantly plants, to be traded across vast distances. During the 8th and 9th centuries CE, the movement of people and knowledge across the Silk Roads facilitated the widespread translation of work from other parts of the world into Arabic, making a broad array of scholarship accessible to polymaths working in the field of medicine in academic centres such as Baghdad and Cairo. As such, Islamic medicine synthesised existing medical knowledge, including that developed in Ancient Greece and Rome, and combined this with knowledge from other regions along the Silk Roads such as China and the Indian subcontinent.
Two medical fields which benefited greatly from the interconnectedness facilitated by the exchanges along the Silk Roads developed considerably during the Middle Ages; medical botany – the scientific study of the medicinal value of plant life, and pharmacology – the branch of medicine concerned with the uses, effects, and modes of action of therapeutic drugs. The development of pharmacology relied heavily on medical botany, a practice which involved cataloguing the many uses and effects of different plants. Amongst the earliest medical botanists were the Ancient Greeks Dioscorides, who produced one of the first pharmacological treatise in the 1st century CE, and Theophrastus (372-287 BCE) who described and classified many additional therapeutic uses of plants.
Pharmacology began to grow considerably in the Middle Ages. When Islam expanded beyond the Arabian Peninsula to the Iranian Plateau, parts of Central Asia, and North Africa in the late 7th century CE, its growth coincided with a golden age of scholarship across the sciences. During this time Muslim and non-Muslim scholars worked from texts translated from Greek, Persian, and Syriac into Arabic. Major advances in the medical sciences were made that built on the knowledge of previous civilizations, such as Greece, Ancient Mesopotamia, and Iran, and incorporated medical knowledge from other regions which reached the Islamic world via the Silk Roads. Because of this, during the height of the Abbasid Caliphate a pluralistic group of brilliant scholars from all over Eurasia were drawn to the court at Baghdad as well as to other academic centres such as Bukhara, Merv, Gundishapur, and Ghazni. Scholars from this period included the physician Razi (845 CE-932 CE), the polymath Avicenna (980-1037 CE), the polymath al-Biruni (973- around 1050 CE), and the botanist and pharmacist Ibn al-Baitar (1197-1248 CE).
These scholars produced many notable texts including Razi’s most famous medical text, ‘The Comprehensive Book on Medicine’ (Kitab Al-Hawi), on which he laboured for 15 years. The text remained unfinished at the time of his death but was later completed by his pupils. This considerable enterprise, comprised of 30 volumes, covered all branches of medieval medicine beginning with a vast overview of the subject including quotations from Ancient Greek and Indian physicians, complemented by the author’s own commentaries and personal observations. Similarly, Avicenna’s ‘The Canon of Medicine’ (Qanun), an encyclopaedia of medicine in five volumes completed in 1025 CE presented an overview of the medical knowledge of the Islamic world, influenced by earlier traditions including Greco-Roman medicine (in particular the works of Galen), as well as Persian, Chinese and Indian medical traditions. Book two of his canon included a detailed list of medical substances accompanied with essays on their general uses and properties.
The exchanges along the Silk Roads played a vital role in much of this scholarship. Despite describing many Chinese medicines in his work ‘Collections of Simple Drugs and Foodstuffs’, the well-known botanist, Ibn al-Baitar, who travelled as far as the Anatolian plateau collecting plants, did not travel to China. Instead, many of the plants he described reached him via the flow of commercial and cultural exchanges along the Silk Roads. Similarly, Avicenna incorporated knowledge of Chinese medicines into his works, writing about the compound ‘suk’ which was thought to treat heart palpitations and protect the liver from damage. Another of the scholars of this time who wrote pharmacological and pharmaceutical textbooks was Muvaffak, who travelled extensively across the Indian Subcontinent researching medical substances and whose work the ‘Book of the Remedies’ (Kitab al-Abnyia), written in Persian between 968-977 CE, contains descriptions and recipes for 585 medicines, including 466 obtained from plants, 75 from mineral substances and 44 from substances of animal origin.
It is important to note that although many of the medicinal plants in these works have since been replaced with modern drugs that are synthesised in chemical processes, a number of the substances identified as having medical properties in the Middle Ages were effective. Humans have used plant based remedies throughout history to alleviate many common conditions including colds, allergies, and digestive issues. For example, although the pain remedy aspirin is now synthesised chemically, a compound similar to the salicylic acid found in aspirin is present in willow bark which was used throughout the ancient world to successfully relieve pain.
These early studies of the medicinal properties of plants and other substances established the groundwork for the modern branch of medicine known as pharmacology. Using information, translations, and materials from various regions across the Silk Roads, scholars compiled pluralistic collections of medical knowledge. These channels of exchange were highly enriching to the development of many fields of science and it is a testament to the exchanges these routes facilitated that considerable amounts of information reached scholars, who had never themselves been to China or the Indian Subcontinent.
The Significance of Cultural Exchange in Alchemy and the Later Development of Chemistry
Interactions across vast distances, such as those which took place along the historic routes of the Silk Roads, have made an undeniable contribution to the enrichment and development of the sciences via the transmission of both knowledge and the material resources for scientific enquiry. Some important proto-scientific disciplines developed along the Silk Roads include medical botany, pharmacology, early responses to infectious disease, and the precursor to the scientific discipline of chemistry – alchemy. Historically, in the case of alchemy and early chemistry, exchange created the conditions favourable to accessing the natural resources required, including the metals and mineral deposits found throughout Central Asia, as well as to diverse bodies of existing knowledge particularly ancient scientific and philosophical texts from Ancient China, Egypt and the Indian subcontinent.
Modern day chemistry is the scientific discipline concerned with elements and compounds composed of atoms, molecules and ions, and their composition, structure, properties, behaviours, and the changes they undergo when they react with one another. It has an incredibly diverse range of practical applications ranging from energy and food production, to building materials, cosmetics, and the development of the medical sciences. Scientific enquiry and method in chemistry had an early proto-scientific precursor in the art of ‘alchemy’, an ancient field of natural philosophy concerned with the purification and perfection of certain materials, the transformation of base metals such as lead into those perceived to be more valuable such as gold, and the creation of panaceas to cure all known illness and disease. Alchemy was a prescientific practice observed throughout many parts of Eurasia and Africa, particularly in China and Europe. It is believed to have been an area of study in China and the Greco-Roman world from as early as the first century CE. Along the Silk Roads, the vast natural deposits of metals in Central Asia encouraged the practice of alchemy and experimentation with metallurgic materials giving rise to an incredibly large number of treatises on the subject.
Although humans began utilising some of the earliest technologies that would go on to form the basis of chemical enquiry from as early as 1000 BCE, such as fire, extracting metals from ores, making pottery and glazes, extracting chemicals from plants for their medicinal properties, making glass, and producing alloys such as bronze, it was not until much later that there were concrete attempts to conduct written studies in chemistry motivated in large part by the potential for uncovering substances with medicinal properties and uses. The earliest written works on chemical process and transformations arose from a number of centres throughout the ancient world, including Egypt, Mesopotamia, the Indian Subcontinent and China.
Later, during the Islamic Golden Age of the 8th to the 14th century CE, Arabic-speaking scholars translated many of these Greek, Chinese, and Indian scientific and philosophical works on alchemy into Arabic in flourishing academic centres such as Baghdad, Cairo, Samarkand and Bukhara. Thereafter, philosophers in the Islamic world pursued chemical and alchemical ideas from across the reaches of the Silk Roads with great enthusiasm and success. The elemental system utilized in medical alchemy was primarily developed by the Persian-Arab alchemist, Ibn Hayyān and was derived in parts from the classical elements of the ancient Greek tradition, namely the four Aristotelian elements of air, earth, fire and water as well as sulphur and mercury. During the mid-10th century CE, Abu Abd Allah al-Khwarazmi created an encyclopaedia of technical terms, Keys of the Sciences (Mafatih al-ulum) in which he described the three constituent elements of alchemy, the apparatus used, the chemical substances required, and their interactions and processing. Indeed, the large number of modern chemical words in the English language which are derived from Arabic, such as alkali, alchemy, zircon, elixir, and many others, attest to the great importance of this period in the development of chemistry as a scientific discipline.
Outside of the many cosmopolitan city centres along the Silk Roads, the origins of chemical and pharmacological knowledge lay in other parts of Central Asia rich in the natural deposits of metals required for experimentation in alchemy. Deposits of raw materials namely lead, silver, and gold in Ferghana and Sogdia, and red salt in the Shahr-i-Sabz regions (in modern day Uzbekistan) were mined extensively. The availability of these natural resources served as the foundation from which alchemy and chemistry could flourish and were transported along the Silk Roads to reach the laboratories of alchemists. From the region, important archaeological finds include apothecary shops and chemistry laboratories dating from the late 8th century CE at excavations in Paikent, Bukhara, in modern day Uzbekistan. Here, various tools and associated technologies have been uncovered, many used in the chemical preparation of medicines such as furnaces, kilns, a hand-mill, glass vessels, and ceramic bowls, valuable items frequently exchanged along the Silk Roads. Many of these glass vessels were a type of apparatus used in chemical distillation known as al-anbiq, from where we derive the name of a distillation apparatus used throughout medieval history the ‘alembic’. Furthermore, a small amount of wax has also been excavated from these apothecaries and laboratories, a substance widely used in Eastern medicine as a component of medicinal ointments.
Indeed, many Scholarly texts regarding the significance of alchemy and chemistry reflected its high profile within the medical sciences of the time. Some examples included, Abu Nasr Mohammad al-Farabi (d. 950 CE), whose treatise, On the Need for the Art of Chemistry was translated into Latin in Europe the 12th century CE. It is an encyclopaedic work that went on to play a significant role in the development of European and Eastern medicine. The polymath and prolific writer Avicenna (980 -1037) revisited the ancient Aristotelean principles regarding the origins of metals and minerals in his work, Book of Healing (Kitab al-Shifa). He believed the theoretical basis of ancient Eastern medicine lay in the principles of mizaj, or the mixed nature of substances, including medicines, which reflected the properties of heat, cold, dryness and wetness. Similarly to the texts written during the Islamic golden age, work produced in Europe during the 12th century CE Renaissance relied on synthesising, via the translation of Medieval Islamic works, existing science and combining it with Aristotelian philosophy and new research. In the development of early modern science in the 16th century, these earlier works on alchemy and chemistry formed the basis of basic laboratory techniques, theory, terminology, and experimental method, some of which bear similarities to that still in use today.
Over time, the transformation and evolution of alchemy led to a more thorough understanding of modern chemistry, pharmacology, and pharmaceutics. Early studies into alchemy, with their attempts to understand the interactions and process of different materials, extract chemicals from natural resources, and synthesise existing knowledge from along the reaches of the Silk roads, established much of the groundwork for the modern science of chemistry. Thanks to the communication networks along Silk Roads, alchemists had access to a vast array of natural resources, including metals and minerals, objects for experimentation like glassware and ceramics, as well as a far reaching network of information available via translation. This allowed for the creation of pluralistic bodies of research, in an environment highly favourable to academic enquiry and knowledge transfer through rich channels of exchange.
Today, the Silk Roads are an instructive reminder that human movement, exchange, and interconnectedness are not solely contemporary phenomenon. Indeed, when it comes to the development of the sciences and technology, we do not occupy isolated worlds but a shared and interdependent one that flourishes when we interact, allowing knowledge to be widely shared. The UNESCO Silk Roads Programme promotes this unique history of cultural exchange and dialogue, which has weaved connections between peoples, and sparked innovation and development across the sciences, and many other fields, for thousands of years, providing the basis for rencounters and exchanges in the contemporary world.