Horses in the Middle Ages were rarely differentiated by breed, but rather by use. This led them to be described, for example, as "chargers" (war horses), "palfreys" (riding horses), cart horses or packhorses. Reference is also given to their place of origin, such as "Spanish horses," but whether this referred to one breed or several is unknown. Another difficulty arising during any study of medieval documents or literature is the flexibility of the medieval languages, where several words can be used for one thing (or, conversely, several objects are referred to by one word). Words such as 'courser' and 'charger' are used interchangeably (even within one document), and where one epic may speak disparagingly of a rouncey, another praises its skill and swiftness.