Armar caballero was a custom of the medieval period in which the King or any other authority granted the dignity of Knight to a person at a ceremony in which dressed him with armor and is hugged him the sword to go to war. Arm means to provide weapons to someone and Knight was and still is a title of nobility.
It is a medieval term. A ceremony that is to follow court rules to achieve, in the middle ages, during feudalism, the title of a knight-errant. Among the ceremonial standards contained the spend the previous night ensuring weapons: that is, without sleep, along with armor and weapons. After he was appointed by his master, with two soft swords on both shoulders and subjected to oath of loyalty to it or to the King.
