The Battle of Tirad Pass, sometimes referred to as the "Philippine Thermopylae", took place during the Philippine–American War on December 2, 1899, in northern Luzon in the Philippines. A 60-man Filipino rear guard commanded by Brigadier General Gregorio del Pilar succumbed to more than 500 Americans, mostly of the 33rd Volunteer Infantry Regiment under Major Peyton C. March, while delaying the American advance to ensure that President Emilio Aguinaldo and his troops escaped.

A rearguard or rear security is a part of a military force that protects it from attack from the rear, either during an advance or withdrawal. The term can also be used to describe forces protecting lines, such as communication lines, behind an army. Even more generally, a rearguard action may refer idiomatically to an attempt at preventing something though it is likely too late to be prevented; this idiomatic meaning may apply in either a military or non-military context.