Based on previously unreleased secret documents from European archives, including the Vatican's, this series unveils the true story of the Catholic Church's 500-year struggle to remain the world's only true Christian religion. For more than half a millennium, a system of mass terror reigned. Thousands were subjected to secret courts, torture and punishment. Spanning medieval France, 15th-century Spain, Renaissance Italy and mid-19th-century Europe, the miniseries reveals how the most powerful church on earth created the Inquisition to attack its enemies and preserve the unquestioned authority of the pope.