According to the Cambridge Dictionary,  annus mirabilus is a year of extremely good events. The term is usually understood to refer to the “miraculous year” of 1666, during which the Great Plague continued and the Great Fire of London raged for as many as four days.  These, as related to a recent article in American Scientist, were certainly not good events, but several contemporary achievements in science were, and the date itself is remarkable.  

Regardless of what happened that year, when written in Roman numerals, the date is distinguished by the curious fact of its being the only year that was or ever will be written as MDCLXVI.  Of course, the same can be said of every year, whether designated by Roman or Arabic numerals, but MDCXLVI possessed what might be considered, at least from a numerological point of view, some more curious significance.  It is the only year containing every one of the Roman numerals I through M only once and in the strict order of decreasing value.  (There is of course another handy rule. Specifically, drawing a horizontal bar over the symbol multiplies it by 1,000. So X¯ would equal 10,000 and ¯V would equal 5,000.  So to write 1 million in roman numerals you’d have to simply write the symbol for 1,000 with a bar over it, namely ¯M.) One thing else to consider is that the descending string DCLXVI or 666, represents to some the Antichrist or the devil, although to Chinese people the number 666 represents good luck.


The Latin adjective mirabilis has been associated with many events for which an adjective such as “amazing,” “remarkable” or one of the synonyms may be fitting.

When the term is used to apply to 1666 or even 1665, it fits remarkably well. In 1665, the bubonic plague, known as the Great Plague, broke out in London and lasted for about two years. (The Great Plague, while devastating, was not as deadly as the Black Death which burned its way across the Eurasian continent from 1347 to 1351.)  

Those Londoners who could afford to move fled the city.  Among those was 23-year-old Isaac Newton.  He had been a student at Trinity College. When the plague struck, he was in the prime of his intellectual life, and according to his own recollection, the years 1665 and 1666 were the most fruitful and creative times. Indeed, according to historian of science Robert Palter, Newton during the plague years figured out that the moon is held in orbit by Earth’s gravity, proved that light is composed of particles, and developed calculus.  

As most of this outburst of genius occurred in the single year 1666, scholars understandably refer to it as Newton’s annus mirabilis.  (I often wonder whether we could achieve anything similar should be allow all of our college students to take a year’s sabbatical.)

Isaac Newton

Many of Newton’s scientific advancements, including his work on optics, made during his time of seclusion were not immediately made public. That is not to say that those achievements were unknown among scientists and engineers, some of whom wished to know more.  

Indeed, in 1684, Newton was visited by three noted fellow members of the Royal Society, including astronomer Edmund Halley, architect Christopher Wren and microscopist Robert Hooke.  

Halley (of comet fame) had catalogued stars in the Southern Hemisphere; Wren was responsible for planning and redesign of much of burned out London;  and Hooke, who used the then novel microscope had observed the cellular nature of matter and microorganisms.)  Each pushed Newton to publish his work and covered all production costs. Halley did the proof reading and editing.

The Great Fire 1666

The Great Fire of 1666 began on a Sunday night in a bakery on Pudding Lane in central London and continued to rage through the following Thursday.  On the first night the streets were thronged and busy as by day, as Londoners ran around with buckets and hand-pumped fire engines spewed water on the spreading flames.  

The destruction died out only after the king ordered that houses be taken down by hand and with gunpowder to create fire breaks. The fire’s toll included more than 13,000 houses (leaving 70,000 persons homeless), 87 parish churches as well as St. Paul’s cathedral and most of the city’s offices. Christopher Wren planned and redesigned the cathedral.

Final Thoughts

In 1966, Robert Palter organized a conference on Newtonian studies that was held at the University of Texas in Austin to commemorate the tricentenary of the year so closely associated with Sir Isaac Newton.  Palter invited historians of science, art, philosophy and religion, along with philosophers of science and practicing physicists.  

They all contributed evaluations of Newton’s world within the framework of modern science.  His accomplishments to a single annus mirabilis may surely be taken as symbolic of a decisive turning point in the history of human thought.

Max Sherman is a medical writer and pharmacist retired from the medical device industry.  His new book “Science Snippets” is available from Amazon and other book sellers. It contains a number of previously published columns.  He can be reached by email at