What Were the Crusades?

Jonathan Riley-Smith's What Were the Crusades is a concise scholarly work by one of the most respected historians of the Crusades, arguing for a specific and influential definition, that crusading should be understood primarily through its formal ecclesiastical and legal apparatus of vow, indulgence and papal authorization rather than only through geography or a loose sense of holy war. Riley-Smith's authority in this field is well established through his broader body of archival work. His functional definition, while highly influential in shaping how the field now periodizes and classifies crusading, is itself a scholarly position that other historians have applied differently, particularly around which later medieval campaigns properly count as crusades under his criteria, an ongoing classificatory debate rather than a settled taxonomy.