Surprise can grant a decisive advantage in battle. Barton Whaley calculated, based on a study of incidents across sixteen wars between 1914 and 1968, that ‘while the usual non-surprise operations produce casualty ratios of about 1-to-1, those with surprise yield ratios of 5-to-1. That is, surprise may be rather reliably depended upon to quintuple the enemy's casualty rates, relative to one's own [sic]’. We lack the data to make a comparable analysis of medieval warfare but Whaley's conclusions demonstrate the impact that a properly conducted surprise attack can have on its victims. It may challenge modern notions of fair and honourable fighting but the evidence presented below indicates that medieval combatants regularly sought to launch precisely these kinds of devastating attacks on their enemies and took precautions to avoid being surprised themselves.

Ambushes: Setting, Executing and Avoiding

Ambushes were ubiquitous in medieval warfare: they account for nearly a third of the incidents in the taxonomy presented in the Appendix. They were simple to arrange: all that was required was a suitable hiding place and sufficient patience to wait for the enemy to appear. If executed correctly, they could confer an overwhelming tactical advantage. The English ‘ambush’ comes from the Old French embusche, which is derived from the Latin inboscāre, a compound of in and boscus, ‘woodland’. Therefore, a literal definition of an ambush would be ‘people concealed in woodland’ to attack an enemy by surprise. Dense woodland can provide cover for a large number of people and was very common in the predominantly rural environment of medieval Europe, which is probably why it became synonymous with surprise attacks. For the purpose of this discussion, I have defined an ambush as any incident in which troops were concealed (in woodland or elsewhere) in order to take their enemy by surprise.

While such incidents are relatively easy to identify in Old French narratives, Latin terminology presents some difficulties. Insidia, which can be translated as ‘ambush’ or ‘ambush party’, can also be used in a figurative sense for any sort of ‘artifice, crafty device, plot [or] snare’.