Spies (Age of Empires II)

Spies is a Technology that can be researched at the Castle. This Technology allows a player to see their enemies Line of Sight. Spies is available in the Imperial Age. The cost of Spies depends on how many Villagers the enemy team has. This Technology is considered the most useful in every Age of Empire game, as it lets you see your enemies movements, however, in later stages of the game, the enemy may have potential dozens of villagers, and this makes the technology extremely costly, sometimes even meaning it is so costly, it is impossible to gather enough gold to research it.