It is one of the most notorious predictions in history, yet a new study challenges the tradition that Julius Caesar was give a month's notice to "Beware the Ides of March".
Analysis of contemporary records of the events leading up to the assassination indicate a doom-laden prophecy was indeed made by the soothsayer Spurinna.
The historian Valerius Maximus recorded that the warning was issued a month before the fateful day, though he only specified the Ides of March - the 15th day of the month - as the date after which the threat would pass.
John Ramsey, professor of classics at the University of Illinois at Chicago, believes Spurinna's initial prophecy was open-ended concerning the date of the danger. The seer then "updated" it to include the Ides and then had his prediction revised once more after the event.
"Spurinna used the traditional means of divination, combined with rumours of plots and discontent, to warn Caesar so far in advance," he said.
The renowned haruspex - a soothsayer who predicted the future by examining the entrails of sacrificial animals - is believed to have made his prophecy in mid-February after cutting open a bull only to find it had no heart.
Ramsey rejects the modern suggestion that Spurinna based his prediction on an astrological horoscope that contained many bad omens. In research published in the journal Classical Quarterly , he demonstrates that the same portents were present in the night sky after the Ides, putting this logic at odds with the historical records.
Instead, he says it is likely Spurinna had simply got wind of one of the plots to assassinate Caesar at this time.
The dictator had just dismissed his loyal bodyguard, adopted the title "dictator for life" and was on the brink of launching a major military campaign against the Parthians. It was well known he would leave Rome at the start of the sailing season in mid-March.
If anyone wanted to kill Caesar, they had only a short while to act.
In this atmosphere, Spurinna was able to make a long-range prediction of possible trouble some time in the coming month. Ramsey believes he refined this to specifically include the Ides only when it was subsequently announced that a meeting of the Senate would be held on that day.
Ancient sources later merged the two predictions, and their reports were later condensed and immortalised by William Shakespeare more than 16 centuries later.