Giordano Bruno, who was embroiled in a long trial which would end with him being burned at the stake in 1600, is sometimes referred to as “a martyr for science”. But he was not.
It is often thought that Bruno was burned because of his support for the Copernican model. The truth is that he really was a heretic, he was burned for his religious beliefs, and it was just unfortunate that the Copernican model got tangled up in the whole business.
The principal reason that Bruno, who was born in 1548, came into conflict with the Church was because he was a follower of a movement known as Hermetism. This cult based its beliefs on their equivalent of holy scripture, documents which were thought in the fifteenth and sixteenth centuries to have originated in Egypt at the time of Moses, and were linked with the teaching of the Egyptian god Thoth (the god of learning). Hermes was the Greek equivalent of Thoth (hence Hermetism), and to followers of the cult he was Hermes Trismegistus, or Hermes the Thrice Great. The Sun, of course, was also a god to the Egyptians, and there have been suggestions that Copernicus himself may have been influenced by Hermetism in putting the Sun at the centre of the Universe, although there is no strong evidence for this.
This is no place to go into the details of Hermetism (especially since the documents on which it was based later turned out not to originate from Ancient Egypt), but to fifteenth century believers the documents were interpreted as, among other things, predicting the birth of Christ. In the 1460s, copies of the material on which Hermetism was based were brought to Italy from Macedonia, and stirred great interest for well over a century, until it was established (in 1614) that they had been written long after the start of the Christian era, and so their “prophecies” were produced very much with the benefit of hindsight.
The Catholic Church of the late sixteenth century was able to tolerate ancient texts that predicted the birth of Jesus, and such thoroughly respectable Catholics as Philip II of Spain (who reigned from 1556 to 1598, married England’s Queen Mary, and was a staunch opponent of Protestantism) subscribed to these beliefs (as, incidentally, did John Dee, Thomas Digges’s guardian). But Bruno took the extreme view that the old Egyptian religion was the true faith, and that the Catholic Church should find a way of returning to those old ways. This, needless to say, did not go down too well in Rome, and after a chequered career wandering around Europe (including a spell in England from 1583 to 1585) and stirring up trouble (he joined the Dominicans in 1565 but was expelled from the order in 1576, and while in England he made so many enemies he had to take refuge in the French Embassy) he made the mistake of visiting Venice in 1591, where he was arrested and handed over to the Inquisition. After a long imprisonment and trial, it seems that Bruno was finally condemned on the specific charges of Arianism (the belief that Christ had been created by God, and was not God incarnate) and carrying out occult magical practices. We cannot be absolutely sure, because the records of the trial have been lost; but rather than being a martyr for science, as he is occasionally represented, Bruno was actually a martyr for magic.
Although his fate may seem harsh by modern standards, like many martyrs Bruno to some extent brought it on himself, since he was given every opportunity to recant (one reason why he was held for so long before being condemned). There is no evidence that his support for Copernicanism featured in the trial at all, but it is clear that Bruno was a keen supporter of the idea of a Sun-centred Universe (because it fitted with the Egyptian view of the world), and that he also enthusiastically espoused Thomas Digges’s idea that the Universe is filled with an infinite array of stars, each one like the Sun, and argued that there must be life elsewhere in the Universe. Because Bruno’s ideas made such a splash at the time, and because he was condemned by the Church, all these ideas got tarred with the same brush. Moving with its customary slowness, it still took the Church until 1616 to place De Revolutionibus on the Index of banned books (and until 1835 to take it off the Index again!). But after 1600 Copernicanism was distinctly frowned upon by the Church, and the fact that Bruno was a Copernican and had been burned as a heretic was hardly encouraging for anyone, like Galileo, who lived in Italy in the early 1600s and was interested in how the world worked. If it hadn’t been for Bruno, Copernicanism might never have received such adverse attention from the authorities, Galileo might not have been persecuted, and scientific progress in Italy might have proceeded more smoothly.
Adapted from my book Science: A History.