The medieval Serbian army was well known for its strength and was among the strongest in the Balkans before the Ottoman expansion. Prior to the 14th century the army consisted of European-style noble cavalry armed with bows and lances (replaced with crossbows in the 14th century) and infantry armed with spears, javelins and bows. With the economic growth from mining, mercenary knights from Western Europe were recruited to finalize and increase the effectiveness of the army, especially throughout 14th century.
History
Early Middle Ages
Between 839 and 842 the Bulgar Khan Presian invaded inland parts of the Serbian territory, the two having lived peacefully sharing a common frontier up until that point. The cause for the invasion is unclear. It led to a war that lasted three years, in which the Bulgars were decisively defeated. In the mid 850s the Bulgarians under Boris I made another unsuccessful attempt to subdue the Serbs. In the beginning of the 10th century Simeon I launched several campaigns against the Serbs who were acting as Byzantine allies and by 925 he managed to conquer Serbia completely but the Bulgarian rule was short-lived. Samuel of Bulgaria subjected the Serbs for a second time in 1009 or 1010 after he defeated their ruler Jovan Vladimir.
10th-century Byzantine military manuals mention chonsarioi, light cavalry formations recruited in the Balkans, especially Serbs, "ideal for scouting and raiding". These units are considered a precursor of Hussar cavalry formations later found in Hungarian and Polish armies.
Late Middle Ages
12th century
The writings of John Kinnamos and other contemporary Byzantine sources (Anna Komnene, Niketas Choniates, Eustathios of Thessalonica, Michael of Thessalonica) of the twelfth century, gives substantial data concerning Serbian armament and tactics.
As primary weapons of the Serbs, Kinnamos mentions spears and long shields. The terms he uses for these weapons (borata and aspibaz) are the words which, in Kinnamos' writings and contemporary Byzantine sources denote spears and shields in general meaning; so, it is not possible to determinate from Kinnamos the type of spears and shields that were used by Serbs of twelfth century. Michael of Thessalonica attests Serbian usage of spears and shields in twelfth century, also by terms of general meaning. Kinnamos mentions Serbian usage of sword. The term he uses for sword (xifoz) is the word which in his writings denotes sword in general meaning; because of that, it is not possible from this term to determinate the type of sword which was used by Serbs of twelfth century. But, in one of his orations, N. Choniates uses word romfaia to name sword used by Serbs. Since term romfaia in Byzantine sources usually denotes one-edged sword, and since Choniates calls sword in general meaning by word xifoz, it is reasonable to suppose that some Serbs of twelfth century used one-edged sword. Surprisingly Kinnamos doesn't mention Serbian usage of bow and arrows, although Serbian usage of arrows is known from the previous epochs. This circumstance may be attributed to fragmental character of Kinnamos' data concerning foreign nations, or to Kinnamos' impression that arrows don't play vital role in Serbian warfare. Kinnamos doesn't mention armor among Serbs, but, when talking about battle of Tara (1150) he says that Serbs were well armed using word katafraktoz which usually means 'armored'. Presence of armor among Serbs of twelfth century could be attested by Michael of Thessalonica who mentions Serbs using mail face-coverings, and we know that such mail masks were usually integral part of mail hauberks. Kinnamos mentions Serbian 'hoplites' in fortress of Galič; since, in Kinnamos writings, term 'hoplite' denotes heavy armed and armored infantryman, this mention of 'hoplite' could also indicate presence of armor among Serbs of twelfth century. Eustathios of Thessalonica also mentions hoplites in Serbian army. Concerning Serbian tactics, Kinnamos also offers interesting fragments. One part of Serbian army fighting in battle of Tara, Kinnamos shows fighting as infantry. Serbian infantry of twelfth century is attested by Eustathios of Thessalonica, but it is important that Eustathios also mentions Serbian cavalry, led by Nemanja. Describing battle of Tara, Kinnamos shows some parts of Serbian army using ambush and sudden strike. Serbian use of ambush is attested by Eustathios of Thessalonica, who mentions Nemanja's ambushes.