Like any other Ranged unit, they work well in firing lines. Under the fire at will command, a good number of Musketeers (50 or more) will provide a constant musket fire, preventing enemies from getting close. Musketeers can also be used as anti-cavalry for a short time. When a battle begins, arrange them in rows quickly and deploy them in a good position in the map, wait for the enemy cavalry to get close before giving them the order to open fire. While waiting for the enemy to get close, arrange your cavalry in attacking formation so that they can relieve the Marksmen when they get overrun by enemy troops.