Spain is home to the world’s oldest active military unit.

Castile regiment, Spanish Civil War

In 1248, King Ferdinand III of modern-day Spain successfully completed the Siege of Seville — part of the ongoing effort to reclaim the Iberian Peninsula from Muslim rule — with the assistance of a plucky fighting group known as the Band of Castile. Said to be impressed by the bravery of this band of fighters, Ferdinand designated it a permanent division under his service, thus inaugurating what is now regarded as the world’s oldest active military unit.

The unit was reorganized numerous times over the following centuries as it took on a series of name changes, from the King’s Guard Colonelcy under Philip IV, to the Regiment of Castile under Philip V, to its current identity as the King’s Immemorial Infantry Regiment. No matter the moniker, the unit has participated in virtually every major conflict in the country’s history, including the 18th-century War of the Spanish Succession and Napoleonic Peninsular War, as well as overseas efforts that both aided the American Revolution and later fought the burgeoning superpower in the Spanish-American War.

Nowadays, the King’s Immemorial Infantry Regiment is largely charged with providing security at the Spanish army headquarters of Palacio de Buenavista, with other members assigned to service in the automobile and music divisions. Many of its duties are ceremonial, such as the palace’s monthly changing of the guard, or the traditional induction of the heir to the throne as an honorary soldier in the unit. While the call to arms is no longer a regular occurrence, this ancient regiment remains ready to aid the monarchy in any way it can, even if that means simply ensuring a smooth drive for palace personnel or fostering good vibes by striking up a jaunty tune.

By the Numbers

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Since World War I, the Swiss Guard has worn some of the world's most colorful military uniforms.

Although the Swiss Guard has been charged with the all-important task of protecting the pope and other denizens of the Apostolic Palace since 1506, one could be forgiven for mistaking this colorfully clad unit for some sort of traveling performance troupe. Its blue, red, and yellow-striped ensemble with a feather-tipped helmet is courtesy of early 20th-century commandant Jules Repond, who studied the frescoes of Rafael for inspiration before publicly unveiling these distinctly Renaissance-era getups in 1915.

These ceremonial "Gala" uniforms are far from the only ones seen around Vatican City; officers don a red velvet outfit for special events, and guards otherwise wear a less-distracting blue tunic in areas with significant foot traffic and even a suit when serving on security detail. Nevertheless, the striped version remains the showstopper for onlookers and a reminder of the prestigious unit's historic roots.