Dear Sir,

Each day on the calendar is the anniversary of some historic event, even if it happened many centuries ago — be it the birth of some noteworthy person, a great battle, a military invasion, an important peace treaty or some other consequential occurrence.

Today’s anniversary (January 11) is a very special one, however, for it was on this date in 49BC that Julius Caesar led his army across the Rubicon River, plunging Rome into a civil war.

By violating Rome’s unwritten rule forbidding generals from bringing their armies into the city, Caesar changed the course of Western history, for the civil war led to the creation of the Roman Empire — Rome had been a republic until then. And the Roman Empire laid the foundation for much of the modern world.

Every day is distinctive in its own way. Today, though, has an extra dimension to it, and that’s worth pausing to reflect on.

BOB DILENSCHNEIDER

New York