Answer: A knight was most valuable to a lord due to their fighting ability, having been sworn to obey a lord and follow them into battle. Medieval battles were brutal hand-to-hand engagements where most fighters were simple peasant levies carrying basic weapons like pikes. A knight, by contrast, had the training to ride a warhorse and the wealth to afford a suit of armor, making them the equivalent of tanks on a battlefield. Knights usually had their own plots of a lord's land, furthermore, so they were also responsible for collecting taxes and maintaining order. Even so, knights were not invincible: the famous Battle of Agincourt demonstrated the weakness of knights against archers, as a muddy hill made it impossible for French knights to reach English archers, leading to a one-sided slaughter.