Astrology was the most widespread and respected of the magical disciplines. It was a great deal more complicated than just dividing humanity up into twelve groups according to their sun signs. The astrologer needed to be a skilled mathematician so that he could calculate the positions of all the stars, major constellations and other celestial features. In ancient Rome, the word for an astrologer was mathematicus and they were a ubiquitous feature of life. Several emperors, both pagan and Christian, tried to keep the astrologers on a short leash, frequently expelling them from the city. The Emperor Tiberius (42BC–AD37) used to invite them to his clifftop villa in Rhodes for a private consultation. As they returned along the precipitous path that was the only way to reach the house, one of Tiberius’s slaves would throw them into the sea. This kept the details of the future emperor’s horoscope completely confidential. One astrologer, called Thrasyllus (d. AD36), foresaw his own imminent demise when Tiberius asked him to predict his future. This impressive piece of prognostication saved Thrasyllus’s life and he joined Tiberius’s household as court astrologer.1 Later emperors were just as touchy about keeping their horoscopes under wraps, and it was a capital offence to try to read the imperial stars.
The Influence of the Stars
Christians always found it difficult to come to terms with astrology. Theoretically, the Bible forbade all forms of divination and there is a celebrated episode in the Acts of the Apostles when new converts burn their valuable books of magic.2 Some Christians denied that astrology worked at all. In the fourth century, St Augustine pointed out that twins, who must be born under the same stars, could often have very different fates. He concluded from this that astrology was bunk, but had to concede that some astrologers did enjoy notable success. However, he said, ‘when astrologers do give very many wonderful answers, this is to be attributed to the hidden prompting of spirits far from good … The astrologers’ success is not due to the art of observing and studying horoscopes, for there is no such art.’3
The complicated calculations required for a horoscope were probably beyond most people in western Europe during the early Middle Ages. However, the new learning from Arab and ancient Greek sources recovered in the twelfth century showed that even the most sagacious ancient authors, including the likes of Ptolemy himself, believed in astrology. Ptolemy had even produced his own astrological manual, known as the Tetrabiblios, and thus lent his enormous prestige to divining with the stars.4 Working from this and other classical sources, Arab writers had produced guides to astrology, which Christian scholars translated along with all their other works. Despite the opposition of Augustine, these Greek and Arab authorities demanded respect and, when they arrived in the West, they brought about a rebirth of the astrological arts.
Even today, no one denies that heavenly bodies do affect events here on earth. The sun is the source of heat and light and even during the early Middle Ages some people thought, correctly, that the moon gives rise to the tides. In the twelfth century, Adelard of Bath discussed and dismissed this possibility in his Natural Questions.5 From there, it is not much of a leap to ask what other effects the planets might have.
There are important differences between the practice of astrology in the Middle Ages and the horoscopes that are found in today’s tabloid newspapers. A medieval astrologer did not place so much emphasis on the twelve signs of the zodiac. These were just a way to chart the movement of the planets. What was much more important was the position of each of the seven planets at the time that the reading related to. The planets, including the sun and moon, move across the sky while the fixed stars provide a background. The sky is divided up into twelve segments (technically called ‘houses’), each one named for the sign of the zodiac prominent within it. Thus, at any time, the position of each of the planets can be defined by which house it is in.
When someone today talks about their star sign, what they mean is the house the sun was in at the time of their birth. Of course, you can’t see the stars when the sun is out, but they are there invisible nonetheless. Everybody knows what their sun sign is, be it Libra, Leo or any of the others. The sun travels through all twelve houses during the course of a year. The moon, on the other hand, completes its orbit of the earth in just under a month and passes through any given sign in two-and-a-half days. For someone to find out their moon sign, therefore, they might need to know the exact time of their birth. We also have a Venus, Mars, Jupiter and Saturn sign depending on where each was in the sky at the time and in the place of our birth.
With all the details of exactly where and when someone was born, there are internet sites that will do the calculations and produce a full list of all the planets and other astrological facts about their birth. Armed with this information, an astrologer claims to be able to tell a great deal about a subject’s personality and the stellar influences on their life. According to astrologers, the sun governs our outward personality. Venus, of course, rules our sex lives and Mars our active lives. In addition, for each of us, one particular planet predominates over the others and determines our personalities. If it is Jupiter we will be jovial, if it is Mercury we will be mercurial (or crafty). We still use these adjectives, along with venereal, martial and saturnine, although they have lost their attachment to astrology. The word ‘lunatic’ originally meant someone governed by the moon.
It is hard to have much time today for people who check their horoscope in the paper in anticipation of it telling them something useful. However, the astrologers of the Middle Ages, even though their art was ultimately redundant, do deserve some respect. They had good reason to believe that the stars influenced the lives of people on earth. The authority of the ancients backed them up on this and their methods required a fine grasp of mathematics. They needed plenty of skill to trace the paths of the planets, even using the astronomical tables that most astrologers relied on. They had to master the astrolabe to tell the exact time, they needed to know their precise location and they had to read an awful lot of difficult material. Of course, many astrologers were just frauds, but we know from surviving books and manuscripts that others worked incredibly hard to decipher messages from the stars.
The most successful astrologers were never short of patronage. One of the earliest practitioners we know about was Guido Bonatti (c.1210–c.1290) who worked under the protection of the Lord of Forli in north-eastern Italy. Reputedly, Guido’s boss would do nothing without first consulting him on the position of the stars. In 1282, troops loyal to the Pope attacked the town of Forli. Guido made an astrological forecast so that he could advise the town’s citizens on the best strategy to adopt against the superior numbers ranged against them. He suggested that a feigned withdrawal would cause the papal army to drop its guard and make them vulnerable to an ambush. The men of Forli did as he suggested and won a famous victory. Guido himself was wounded in the battle as he treated his fallen comrades. He assured his worried compatriots that he had foreseen his injury and would make a full recovery.6
Although Guido Bonatti did not suffer for his astrological interests while he was alive, they did his subsequent reputation no good at all. When Dante Alighieri wrote his Comedy in the early fourteenth century, he condemned Guido to hell for divining with the aid of demons. He was cursed to spend eternity with his head twisted around backwards as punishment for seeking too earnestly to look forward into the future.7 Nonetheless, despite its author’s confinement to hell, Guido’s guide to astrology remained a standard work until the seventeenth century.
Monarchs were also keen to have the stars on their side. In 1235, the Holy Roman Emperor Frederick II (1194–1250) acquired a young English bride. However, with admirable self-control, he resisted consummating the marriage until his astrologers told him it was a propitious moment to conceive a son. The stars did not lie and nine months later, an heir to the imperial throne was born.8 Frederick was renowned for his patronage of the sciences. Among other achievements, he legislated to regulate the medical profession, set prices for drugs and wrote a remarkable study of birds.9 His learning was so broad that he was called ‘the wonder of the world’, although the papacy, with which he was in constant conflict, did not agree.
Initially, the Church tended to follow the lead of St Augustine and disapproved of astrology because of its diabolical connotations. The astrologers defended themselves by insisting that, on the contrary, the planetary influences were simply natural forces that it was entirely legitimate to investigate. That being the case, there was not very much for the Church to object to. As astrology became more widespread, clerical opinion grew increasingly lenient. Thomas Aquinas considered the matter carefully. His views represent something approaching the medieval consensus and are worth quoting:
If anyone attempts from the stars to foretell future contingent or chance events, or to know with certitude future activities of men, he is acting under a false and groundless presumption, and opening himself to the intrusion of diabolic powers. Consequently, this kind of fortune telling is superstitious and wrong. But if someone uses astronomic observation to forecast future events which are actually determined by physical laws, for instance drought and rainfall, and so forth, then this is neither superstitious nor sinful.10
So, as far as the Church was concerned, the science of astrology was acceptable when it was restricted to studying the natural effects that the stars have on earth. In that case, the astrologer could not see the future but could make forecasts based on the predictable motions of the heavens. However, true divination was not possible using purely natural means and hence was out of bounds to good Christians.
The Church also drew other lines that no astrologer should cross. A highly controversial question in the Middle Ages was whether the stars could fix people’s fate or just exert an influence. Aquinas was sure that it was the latter:
The stars and planets and their courses cannot directly cause the choices of man’s freewill. Still, they can dispose and incline man to do this rather than that, in as much as they make an impression on the human body.11
This was important because if the facts of our birth determine the course of our lives, any idea of free will or moral responsibility becomes untenable. The Paris condemnations of 1277 made it very clear that as far as the Church was concerned, fate was not fixed and the stars could only effect predispositions.12 The whole debate over astrological determinism closely resembles the argument about nature versus nurture that is raging today. Are our personalities determined by our genes or do the decisions we make in life affect the kind of person that we are? Substitute the stars fixing your fate at birth with your parents’ genes doing so at conception, and the whole question of determinism becomes an urgent twenty-first-century concern. Like the Church in the Middle Ages, most of us are acutely uncomfortable with the idea that free will might be an illusion.
The medieval Church repeatedly attacked determinism and defended the concept of free will.13 No one could be in any doubt that it was not merely wrong to say that we cannot escape our destiny, it was heretical. Inevitably, some astrologers would not toe the line and one or two galloped imperiously across it. Cecco D’Ascoli (c.1269–1327), a lecturer on astronomy at the university of Bologna, was one of these.
The Terrible Fate of Cecco D’Ascoli
Bologna in the fourteenth century was a city of lofty towers. When a Bolognese family wanted to keep up with the neighbours, they had to ensure that their tower was taller than the one next door. Few of these architectural monstrosities survive today but the Torre degli Asinelli, one of those that does, is an impressive 300 feet high. In Cecco D’Ascoli’s day, there were hundreds of these turrets dotted around the city as ostentatious displays of the leading families’ wealth. The university was thriving as well. It was already over two centuries old and had added a medical faculty to the original law school. Students who wanted to study medicine were expected to master Aristotle’s natural philosophy and basic mathematics before they started the medical course proper. Although Cecco was a lecturer on astronomy, for students training to be physicians, in fact astrology was the rationale for learning about the stars. It is no surprise, then, that it was as an astrologer that Cecco built his reputation.
The text that he used for his classes was The Sphere by Englishman John Sacrobosco (who died around 1256). About Sacrobosco himself we know next to nothing except that he spent most of his career teaching at Paris. His book is a short and simple introduction to the knowledge of the heavens that was current in the thirteenth century, specifically intended for students at the new universities. The title refers to the fact that medieval people, like the ancient Greeks, thought that the universe was perfectly round, with the earth at its centre. Because The Sphere was so brief, lecturers tended to use it as a jumping-off point rather than treating it as an exhaustive survey. Its brevity also meant that Sacrobosco’s book was extremely adaptable, and university lecturers were still using it in the early seventeenth century.14 Not until it became widely accepted that the earth was not at the centre of the universe did The Sphere finally face obsolescence.
Cecco D’Ascoli was among the lecturers who went well beyond the basics laid out by Sacrobosco. He put his own astrological spin on the material and appended many other unrelated ideas. Sacrobosco himself does not mention astrology at all. Among the additional material that Cecco added to spice up his lectures was speculation about astral spirits and other even more risqué aspects of magical lore. When he actually gave the lectures, he may have gone even further than he was willing to admit in his published writings.
The professors of Bologna were respected and reasonably well paid, but Cecco had a lucrative sideline that allowed him to live very comfortably indeed. He traded on his reputation as an astronomer to moonlight as an astrologer, providing readings for clients who wanted to know their future. Cecco was in no doubt that astrology worked and that the stars were a sure guide to what lay ahead. He crossed the threshold of acceptable opinion, holding, contrary to the Church’s instructions, that events on earth were absolutely determined by the position of the stars. His confidence in astrology caused him to make statements that even today seem shockingly foolish in their bravado. In an incredibly unwise move, he went as far as to calculate the horoscope of Jesus Christ. The result of his calculations, he declared, showed that the reason for Jesus’s lowly birth and violent death was his being born under malevolent stars.15 This was explosive. Under the doctrine of the Trinity, Jesus was God incarnate. By claiming that the Messiah’s life was determined by the arrangement of the heavens at his birth, Cecco was subjecting the very Deity to the stars.16
Rumours of what Cecco was up to leaked out. We do not know if his students or his clients betrayed him, but someone found his pronouncements beyond the pale and reported them. The man who was most interested in such deviancy was the local inquisitor for Bologna, one Lambert de Cingulum (fl.1316–24). Like many inquisitors, he was a member of the Blackfriars, the Dominicans of Thomas Aquinas. This meant that he was no ignorant cleric frightened by things he could not understand. Lambert was an educated scholar, an expert on the ethical teaching of Aristotle and a professor in his own right.17 He probably knew Cecco personally.
Like the secret police in a communist state, inquisitors depended on a network of informers and agents to keep them abreast of heresy in their district. The system was wide open to abuse by those who denounced their enemies for personal or venal reasons. An inquisitor was trained to be aware of this possibility and punish those who made false accusations. We cannot tell if Cecco was the victim of a vendetta or jealousy but nevertheless Lambert had little difficulty in finding him guilty of making heretical statements. In 1324, he stripped Cecco of his lectureship, fined him £70 and imposed a penance that he should listen to a large number of sermons over the following year. The size of the fine indicates that the crime was a considerable one and that Cecco was wealthy enough to pay it. Above all, Lambert forbade Cecco to continue either studying or practising astrology.18 We should note that even for such a heinous offence as subjecting God to the zodiac, the inquisitor did not imprison, let alone execute, Cecco. This tells us the inquisitor was satisfied that the defendant had come clean and admitted to all his crimes. When summoned before an inquisitor, any strategy other than complete candour would be a serious and probably fatal mistake.
If only Cecco had stuck to mainstream astronomy from then on, he could have continued his career without much of a stain on his character. In time he would have expected to get his job back and been reintroduced to polite society. Unfortunately, he would not stop reading the stars. He left Bologna and travelled to Florence where he set up shop as a freelance astrologer. There are plenty of later and unreliable stories about what he got up to and how he made enemies of important people. None of them is necessary to explain what happened next. Inquisitors communicated with each other and it only took a couple of years for Cecco’s past to catch up with him.
The inquisitor of Florence was a Franciscan friar called Accursius. He locked up Cecco in 1326 and then sent a messenger to Bologna asking for details of the previous trial and a copy of Cecco’s book of lecture notes. Accursius was nothing if not meticulous and spent a year carefully investigating the case. This thoroughness was necessary for a very simple reason – Cecco’s crimes were now of a capital nature. We have seen how the inquisitors would not hand a heretic over to the secular arm of government for their first offence but were utterly merciless to repeat offenders. By continuing to practise astrology, Cecco had deliberately flouted a direct order from an inquisitor. If found guilty there would be no clemency. Eventually, Accursius satisfied himself that the evidence against Cecco was watertight. A court session in the Franciscan Church of Santa Croce in Florence found that he was a recalcitrant heretic and ordered that he be handed over to the secular authorities. As the prisoner was led out, he would have passed close to the Barbi chapel where the paint of Giotto’s sublime fresco cycle on the life of St Francis of Assisi was barely dry. The same society that could create such tenderness and beauty on wet plaster could also send a man to an agonising death for a crime we hardly recognise. The great piazza in front of the church lay just outside the city walls. There Cecco was burnt on 16 September 1327.
Cecco and his peers had good reason to believe that they lived in a world where their art might have a physical basis. Even so, astrologers certainly had an interest in promoting the reliability of what they did. The influence of the stars may have been pure moonshine but the money to be made was quite substantial. Importantly, astrology also provided astronomy with an application beyond mere curiosity and a vital market for astronomical tables.19 This led to demands for improved accuracy and encouraged the study of Greek works newly translated from Arabic. Only because astrology meant that it could be lucrative to do so did anyone bother to master Ptolemy’s fiendishly difficult Almagest. Unless astronomy was a skill that brought with it the ability to earn hard cash, there was little point in learning it. The disinterested pursuit of useless knowledge was not something to which many people were rich enough to aspire.
The Philosopher’s Stone and the Elixir of Life
Astrology’s twin erstwhile science was alchemy. Everybody knows that alchemists were trying to transmute base metals into gold but there was a great deal more to it than that. To perform transmutation, they needed first to generate a special substance to act as a catalyst. This was called various names such as the ‘Elixir’ and the ‘Philosopher’s Stone’. Attempting to produce it was the principal aim of the alchemists’ art and they attributed all sorts of wonderful properties to the elusive substance.
Alchemical texts tend to be confusing, contradictory and deliberately obscure. However, on one thing they all agreed – the subject should always be approached with a pure heart. The quest for the philosopher’s stone was, like the search for the Holy Grail that was developing in contemporary romantic literature, only for those of the highest moral integrity. Those who were just out to make money would surely fail. This was sage advice, as alchemists were notorious for losing fortunes in their research. Many medieval writers satirised the fact that alchemists were far more adept at spending gold than creating it. Why, Georg Agricola (1494–1555) asked in his treatise on mining, is there no such thing as a rich alchemist?20 Geoffrey Chaucer teased them in the Canterbury Tales. His Canon’s Yeoman despairs of ever finding the philosopher’s stone:
We seek and seek, and were it once discovered
We should be safe enough, expenses covered.
But there is no way; whatever paths we trod
The search was useless and I swear to God
For all our cunning, when all’s tried and done
That stone won’t yield itself to anyone.21
We can learn something of the theory of alchemy from a reasonably clear guide, supposedly written by Albert the Great, that lays out the process by which transmutation was supposed to take place. Mercury, pseudo-Albert writes, is ‘the source and origin of all metals’. Other substances, including sulphur and arsenic, act as a sort of tincture to the quicksilver. The alchemist, through his experiments, is trying to manipulate the composition of a base metal to produce gold or silver. Pseudo-Albert provides further precepts that the fledgling alchemist should follow. He advises secrecy, a special laboratory and the use of glass apparatus. Finally, he reiterates the need to have a good supply of funds.22
Alchemy’s poor reputation was mainly caused by concern about fraudulent activity in which crooks passed off fake gold as the real thing. In 1317 Pope John XXII (1249–1334), who ironically has an alchemical treatise ascribed to him, issued a decree against those who claimed that the gold they pretended to have created was genuine. While the decree does not outlaw alchemy in itself, it certainly denies the possibility of actual transformation. Alchemists are unable ‘by the very nature of things’, said the Pope, ‘to produce real gold or silver.’23 More sympathetically, Thomas Aquinas analysed the question of whether an alchemist could honestly sell the gold he created. He concluded that ‘if genuine gold could be chemically produced, it would not be illicit to sell it as true gold, for there is no reason why science should not exploit natural causes to produce natural and true effects.’24
Philosophers also doubted the effectiveness of alchemy. The Muslim writer Avicenna had been certain that alchemy would never work because it was logically impossible for mankind to improve on nature. His attack was not just on alchemists, but on all kinds of technology and machinery.25 Secular rulers, on the other hand, were prepared to hope there was something to it. Henry VI (1421–71) of England granted licences to people who said they could make gold at will, seemingly unaware of the inflationary problems this would engender for his economy.26
No one has yet been able to transmute base metals into gold. But medieval alchemists did make some quite impressive breakthroughs in the course of their research. Foremost among these was the discovery of acid. There are three main acids, hydrochloric, sulphuric and nitric. Together, these are known as the mineral acids because they are relatively easy to produce from the right sort of ore. Nitric acid was particularly exciting because it could be used to dissolve gold – a feat ascribed to Moses in the Bible.27
The acids, as well as alcohol, appear to have first been isolated by Christian alchemists in the thirteenth century using a technique called condensation,28 but for many years it was assumed that the Arabs had produced them much earlier. We now know that this misconception was caused by Christians attributing their texts to Arabic writers. We’ve already seen the tendency of esoteric manuscripts to be ascribed to a famous author to increase their credibility. Alchemists were particularly prone to this and their favourite pseudonym was the Arab savant Geber, who was active in the ninth century. It is far from clear that any of the works ascribed to him are genuine, but the accretion of titles to his name has led to him being credited with all sorts of innovations, such as the distillation of acids, which he did not actually make.29
Gold was beyond them, but late-medieval alchemists did extend the range of metals beyond the seven known to the classical Greeks. By the sixteenth century they had isolated the metallic elements of zinc, bismuth and antimony as well as others that the extant documentation makes hard to identify.30
Besides the production of new materials, the major achievement of alchemy was in the field of techniques. Their experiments led to the perfection of distillation and calcinations, not to mention the development of the glass apparatus required to carry out these operations.31 The methods were handed down through the generations until the eighteenth century when the experimental method began to make itself felt in chemistry. In order to make serious progress, chemists had to learn the discipline of careful quantitative measurement, especially the weighing of materials before and after chemical reactions. During the Middle Ages, no one seems to have had the patience or skill to carry out such exacting work.
The common ground shared by the arts we have discussed in this and the previous chapter – magic and medicine, astrology and alchemy – was their reliance on occult forces. Magic favoured a holistic view of the world which supposed that invisible threads linked the heavens and earth, macrocosm and microcosm, into a tight web of influences. The stars emitted rays, the astrologers claimed, by which they affected the lives of men. The properties of metals were the result of hidden forces that worked within them. Control the forces, said the alchemist, and you could transform the materials. Even the learned doctor studied the active qualities within herbs that could heal an afflicted body.
Nowadays, the word ‘occult’ specifically means ‘magical’ or something connected to spiritualism. But it used to have a much wider sense, connoting any force or property that was hidden. Put bluntly, if you cannot see it, it could be classed as occult. Aristotle had little time for the concept and argued that all effects must be material. One thing, he said, can only affect another by touch. Modern science rejects this absolutism and recognises all sorts of actions at a distance, from gravity to magnetism. Aristotle had his own explanation for gravity, which we will come to in chapter 9, and he ignored magnetism. For a long time, that didn’t matter too much because magnets were rare lumps of rock and hardly a reason to overthrow the laws of physics. Then, in the thirteenth century, they became rather more important. As we will see in the next chapter, the Arabs heard about a new navigational instrument from the East and before long it arrived in western Europe. This was, of course, the magnetic compass.
Perhaps the medieval attitude of suspicion rather than outright hostility towards astrology and alchemy, typified by the Church, struck the right balance. This prevented the magical worldview from dominating the alternatives while allowing the practical aspects of astrology and alchemy to feed through into modern scientific thinking. However, as we will now see, it was in the fields of natural philosophy and technology that progress was most marked in the later Middle Ages.