Although the term infantry dates from the 15th century, the foot troops of the previous eras in history who fought with a variety of weapons before the introduction of the firearms are also referred to as infantry. During the Ancient and Middle Ages infantry were often categorized by the types of weapons and armour they used, such as heavy infantry and light infantry. Generally, light infantry acted as skirmishers, scouts, and as a screening force for the more heavily armed and armored heavy infantry, the latter of which often made up the bulk of many historic armies.