Age of Empires II: Definitive Edition (PC) - Achievement - Golden Spurs
Transform 50 Villagers by researching Flemish Revolution.
Flemish Revolution is a Burgundian technology that is researched at the Castle and becomes available in the Imperial Age. If you are playing through the Lords of the West Expansion, the first mission it becomes available to do on is The Wolf and the Lion - the 2nd level. It turns all of your villagers in to Flemish Militia. They become military infantry units and lose the ability to harvest resources. You need to make sure you have at least 50 villagers before researching the technology in order for the achievement to trigger.