Lumber

Lumber is one of the five main resources in the game, next to food, iron, stone, and gold.

Lumber is consumed by the following actions:
 * Construction of buildings
 * Construction of fortified units
 * Researching technologies
 * Troops training

Acquisition
Lumber is produced by Sawmills, but it can also be won on the Wheel of Fortune, or farming NPCs for resources. If done correctly, large amounts of lumber can also be acquired by trading with resource (i.e. buying a resource for a cheap price and selling it for a more expensive price).