Medieval warfare is the warfare of the Middle Ages. In Europe, technological, cultural, and social developments had forced a dramatic transformation in the character of warfare from antiquity, changing military tactics and the role of cavalry and artillery. In terms of fortification, the Middle Ages saw the emergence of the castle in Europe, which then spread to southwestern Asia.

si vis pacem, para bellum
If you want peace, prepare for war

Publius Flavius Vegetius Renatus, Vegetius for short, wrote De re militari possibly in the late 4th century. Described by historian Walter Goffart as "the bible of warfare throughout the Middle Ages", De re militari was widely distributed through the Latin West. While western Europe relied on a single text for the basis of its military knowledge, the Byzantine Empire in southeastern Europe had a succession of military writers. Though Vegetius had no military experience, and De re militari was derived from the works of Cato and Frontinus, his books were the standard for military discourse in western Europe from their production until the 16th century.De re militari was divided into four books: who should be a soldier and the skills they needed to learn; the composition and structure of an army; field tactics; how to conduct and withstand sieges, and the role of the navy. According to Vegetius, infantry was the most important element of an army because it was cheap compared to cavalry and could be deployed on any terrain. One of the tenets he put forward was that a general should only engage in battle when he was sure of victory or had no other choice. As archaeologist Robert Liddiard explains "Pitched battles, particularly in the eleventh and twelfth centuries, were rare."