The word "Gaesatae" is Celtic for "Spearmen". This implies that the Geasatae warbands could have fought either in a phalanx or that the spear was their primary weapon instead of the sword.

The Gaesatae Order was most likely founded in the 4th Century BC in Gaul. The Gaesatae offered their services to other Celtic tribes or anyone who needed men to fight. The Gaesatae are most renowned for their service for the Celts in the Po Valley, such as the Boii and Insubre tribes. They provided around 15,000 men at the Battle of Telamon and fought alongside the Insubres at the Battle of Clastidium. After the Gallic War of 225 BC to 223 BC, the Gaesatae fade away into history. They most likely had warbands in Gaul during the Gallic War of 225 BC to 223 BC, and took part in local tribal wars until the military order died out in the mid 2nd Century BC.