Knighthood is a Technology in Age of Empires III that can be researched in the Capitol building for 1500 food. The upgrade increases the hitpoints of heroes (i.e., Explorers) by 1000.

This technology must be researched before Peerage becomes available.

Capitol technologies
Blockade | Spies | Knighthood | Peerage | Immigrants | Large Scale Agriculture | Deforestation | Excessive Taxation | Legendary Native Warriors