On January 10, 49 B.C., on the banks of the Rubicon River in southern Gaul (near the modern-day city of Ravenna), Julius Caesar and the soldiers of the 13th Legion waited and weighed their options.

Forty-nine years before Jesus of Nazareth was born in Bethlehem, Roman general Julius Caesar and his army crossed the river Rubicon—the waterway separating Gaul (modern-day France) and Italy. They ...