The Writer’s Guide to Raising a Medieval Army
Wars and battles are all well and good in fantasy, but to fight them, you first need an army. But how can your protagonist convince a group of people to put their lives on the line? Throughout history, armies have been raised through various methods and they varied in size, skill, equipment, and dedication.
As always, magic is the exception to the rule. Because magic.
Calling Up Vassals
The most common method of raising an army in medieval Europe was to call up your vassals. The feudal system was a web of alliances and oaths of loyalty and service. At the top was the king, or sometimes the queen. He would call upon the nobles who had promised their service. Usually, this was in return for land and titles. The nobles would call upon their vassals, who would call upon their vassals. Lower-level vassals may only muster a dozen men, but when combined with everyone else called up, those numbers added up at an army. In the book series, The Song of Ice and Fire, George R. R. Martin uses the term “calling the banners.”
The king could also openly call for soldiers and men who were not obligated to serve under the feudal system could volunteer. This method is how many English archers were recruited during the Hundred Year’s War. Village militias and other regional military groups were common, especially along frontiers, and could be recruited into larger armies.
Armies could also be formed by a large group of people rallying to a common cause. The Crusades are a prime example. The pope put out a call for soldiers and people from across Europe, and every social class answered.  There was even an army of children in 1212 known as the Children’s Crusade that recruited across Germany and France.  I have covered other examples in previous articles such as the army raised by Boudica against the Romans and the peasants revolting against the cruelty and corruption of the nobility and clergy in the German Peasants’ War.
Although standing armies have become the norm today, in the Middle Ages, they were uncommon. They existed in antiquity, the most notable being that of the Roman Empire, but they were expensive. The expense could be offset by a large economy or by constantly conquering new resources.
Another problem was that they caused problems when they were bored. A standing army with nothing to do led to several Roman emperors being assassinated or overthrown. One way to mitigate this problem is to keep the army constantly busy. The Romans achieved this through near-constant expansion. The Holy Roman Empire in the 15th to 17th centuries came up with another solution. When not at war, they let their soldiers, known as landsknechts, hire themselves out as mercenaries under the condition that if the emperor ever called them up, they would return to fight for him. They were also prohibited from taking any contracts to fight against the emperor. This kept them busy but available when needed. However, this solution wasn’t perfect. One unit of landsknechts, known as the Black Band, refused a recall from the emperor and was killed almost to a man by loyal landsknechts at the Battle of Pavia.
Free Companies and Mercenaries
If your protagonist doesn’t have access to a standing army and can’t raise one through feudal obligation or common cause, they can always buy one. Mercenaries and free companies were common in medieval Europe. Free companies were professional military units for hire while mercenary was a term for hired thugs. Free companies were used in peacetime and war as city guards and police forces. With mercenaries, once they did what you had hired them for, you wanted them to go away.
The downside to using soldiers for hire is that they can turn on their employer. Violent betrayals were frequent, especially in Italy during the 16th century. In his book The Prince, Niccolò Machiavelli argues against the use of mercenary armies for this very reason.
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Copyright © 2022 Rebecca Shedd. All rights reserved.
 Duncalf, Frederic (1969). "The Councils of Piacenza and Clermont". In Setton,K., A History of the Crusades: Volume I. pp. 220–252.  Russell, Frederick H. (1989). "Children's Crusade". In Strayer, Joseph R. (ed.). Dictionary of the Middle Ages. Vol. 4. New York: Charles Scribner's Sons. pp. 14–15.