With Arthurian grandeur the Papal Zouaves marched into Italy in the mid-nineteenth century, summoned by the Pope under siege as the Wars of the Risorgimento raged. Motivated by wanderlust, a sense of duty and the call of faith, some 20,000 Catholic men from around the world rallied to Vatican City to defend her gates against Sardinian marauders. Volunteers came from France, Belgium, Spain, Ireland, Austria, and many other countries, including the United States. The battles that ensued lasted over 10 years, among a shifting array of allies and enemies and are among history's most fascinating yet largely overlooked episodes. Napoleon, Pius IX, and Bismarck all make appearances in the story, but at the center were the Zouaves—steeped in a knightly code of honor, and unflinching in battle as any modern warrior—as the Church they vowed to defend to the death teetered at the brink of destruction.