Warfare was a constant part of life in Germanic societies. It should not be understood, however, as a series of continuing conflicts between state structures, like modern warfare, but rather as based on feuds between families, armed rivalry between clans and their followers, and warfare which drew in broader tribal elements.

Written sources on the nature of Germanic warfare are scant and ambiguous. The most informative are Tacitus, Germania, chapter 6 (c. ad 98), and the Strategicon of Maurice Book 11 (c.570–630), as well as occasional descriptions of Roman–Germanic encounters, such as Ammianus Marcellinus’ account of the Battle of Strasbourg (Argentorate) in 357 (XVI, 12).

These sources, combined with archaeological finds, suggest that the level of tactical organization among Germanic societies during Late Antiquity was rather low. The preferred method of attack was to attempt to destroy the enemy’s formation by deploying archers, infantry with little or no body protection, and mounted warriors in fast-advancing surprise attacks. Late Roman writers considered these tactics wild and disorganized. No reliable data can be found on the preferred battle order, though wedge-like formations such as the boar’s snout (caput porci: Vegetius, III, 19; Ammianus, XVII, 13, 9; Agathias, II, 8, 8) and lined arrays (phalanx: e.g. Orosius, VI, 7, 8, drawing on Caesar, Gallic War, I, 52) are both described in the sources. Battles themselves were thought to be decisive, their outcomes binding: the battlefield was perceived as physically circumscribed, and the victorious army was entitled to claim men, horses, and equipment from it.

Descriptions of raids, both terrestrial and maritime, show that Germanic armies were capable of covering large distances in a short time. Evidence for sieges of larger settlements is sparse, and mostly concern attacks on Roman territory. However, defensive works known from 1st- to 6th-century northern Europe include long walls and ring fortresses. Barbarian armies of up to 2,000 men headed by a single leader are conceivable for Central Europe in the 3rd and 4th centuries, and in special circumstances short-lived alliances could bring together larger armies, such as the confederation which fought the Battle of Strasbourg. Methods of recruiting, preparation, and tactics for fighting the Romans were different from those required for fighting other barbarians.

Sea transport of troops in the Baltic and along the North Sea coast is evidenced by finds of ships and ship parts of the Nydam boat type rowed by 20–30 men. These were deployed against both Romans and other barbarians. In the 3rd and 4th centuries large sea barricades protected Danish fjord inlets from seaborne attacks, and raiding on the coasts of Late Roman Gaul and Britain made necessary the system of defence along the North Sea and English Channel which was commanded by the Comes of the Saxon Shore.

Warrior aristocracies were important in the life of Germanic societies. Martial topics are represented in early personal names, in images, and in the earliest Germanic literature. Ulfilas’ translation of the Bible into Gothic omitted the OT Books of Kings, because they might have served to foment smiting and justify strife (Philostorgius, HE II, 5). Warfare was also closely connected to religious rituals, as is apparent from the large weapon deposits from the 4th century bc to the 6th century ad, at, among other sites, Illerup and Nydam. Elsewhere, conversion to Christianity could be consolidated by the God of battles.