What is the Ides of March? History behind the ominous date explained

Each year, March ushers in celebrations of St. Patrick's Day, the start of spring and Women's History Month. It also comes with an ominous warning: "Beware the Ides of March."

The phrase comes from William Shakespeare's "Julius Caesar," in which a soothsayer delivers the infamous warning to the Roman emperor before his assassination. Shakespeare relied heavily on the work of the Greek historian Plutarch to craft his play, and the real Caesar may have been given a similar warning before he was assassinated on March 15, 44 B.C.E.

The play was one of Shakespeare's early tragedies, and the line would have resonated with those in his audience who were well versed in the history of the Roman Empire, according to Eric Rasmussen, a Shakespeare scholar and an English professor at the University of Nevada, Reno.

"The entire audience would know that, oh yeah, the 15th of March, that's going to be now the day that he's assassinated," Rasmussen said.

What is the Ides of March?

Roman calendars defined days using three markers: the Ides, Kalends and Nones, according to Dwayne Meisner, a classical studies instructor at Campion College at the University of Regina in Canada. The first day of the month was called the Kalends, the middle of the month was the Ides and the Nones fell between them, Meisner said.

"Whatever part of the month you were in, it's either X number of days until the Kalends, or the Nones or the Ides, and that's how you knew what day of the month it was," Meisner said.

Meisner said the Romans counted time this way while using the lunar calendar and continued to do so after Caesar created the Julian calendar, which is based on the solar year and included a leap day every four years.

When is the Ides of March 2025?

The Ides of March falls on Saturday, March 15, 2025.

What happened on the Ides of March?

Since Caesar's assassination, the Ides of March has been used as the title of movies, songs and episodes of television. And several other ominous events have occurred on that day.

On March 15, 1889, seven American, German and British warships sat in a standoff in the harbor of Apia, Samoa, as a civil war raged. The standoff ended when a deadly cyclone hit the harbor damaging six of the ships and killing approximately 200 people, according to Naval History and Heritage Command.

On March 15, 1939, Adolf Hitler moved Nazi troops into Czechoslovakia, annexing the country and ending the practice of appeasement. Later that year, Britain declared war on Germany, sparking World War II.

On March 15, 2003, the World Health Organization declared SARS a "worldwide health threat." Over the course of the outbreak, more than 8,000 people were sickened and nearly 800 died in over 37 countries.

Contributing: Gabe Hauari, USA TODAY