The Heruli (also Eluri, Eruli, Herules, Herulians) were one of the smaller Germanic peoples of Late Antiquity. Along with their neighbours the Scirii, Rugii and Gepids, they are known from the third to sixth centuries. In the late 5th century AD and early 6th century they lived in a series of relatively small kingdoms established near the Roman frontier along the Middle Danube. At first they established a kingdom north of Vienna, which they were later able to expand southwards towards Lake Balaton, and eastwards towards the Tisza. After the conquest of this kingdom by the Lombards in 508, smaller groups were established in Sweden, Ostrogothic Italy, and present-day Serbia, which was under Eastern Roman control.
After the death of Attila in 453, the Danubian Heruli fought in the Battle of Nedao in 454, although it is not certain which side they took among his various former allies. They also participated in successive conquests of Italy by Odoacer (476), Theoderic the Great (493), Narses (554), and probably also the Lombards (starting in 568). After their independent kingdom was destroyed by the Lombards in 508, a part of the Danubian Heruli subsequently became established inside the Roman empire near Belgrade, and continued contributing fighting men to the Eastern Roman Empire, and participating in Balkan and Italian conflicts. With their last kingdom eventually dominated by Rome, and smaller groups integrated into larger political entities such as the Gepids and Lombards, the Heruli disappeared from history around the time of the conquest of Italy by the Lombards. In this period the Middle Danube was coming under the control of the Pannonian Avars.
The Danubian Heruli are believed to have moved from Ukraine during the 4th century, like their neighbours the Goths and Alans, forced to move the entry of the Huns into Europe from the east. They are thus generally equated to the "Elouri" who lived near the Sea of Azov in the third century, and took part together with Goths and others in massive raids into Roman provinces in the Balkans and Aegean Sea, attacking not only by land, but notably also by sea. The equation of these "ELuRi" with the "ERuLi" was made by several Byzantine authors, and is still widely accepted. However, some scholars such as Ellegård consider such proposals uncertain, and have proposed that the Heruli homeland may be have actually been near the Middle Danube. In contrast, because a group of Danubian Heruli moved from the Danube to Scandinavia, some scholars believe that the Heruli had their earliest origins in Scandinavia, and that there may have been Heruli kingdoms in several parts of Europe. (Similar northern origins are also often proposed for the Goths and Rugii, and other Germanic peoples.)
Like the Goths, soon after first being noted in contemporary records for their raiding the Heruli began entering the Roman empire and serving in its military, where they developed a particularly notable reputation already in the 4th century, at first mainly in the Western Roman Empire, where they were already mentioned in the late 3rd century. It has even been proposed that a western Heruli settlement existed somewhere near the Lower Rhine in this period, under Roman influence. Heruli were in any case settling somewhere near the Roman frontiers, and they were among the many groups causing disruption inside and outside of the empire in this period. In 405 or 406 Heruli were among the ferocious nations who Saint Jerome described as occupying all of Roman Gaul. Attila and his Huns were moving east and came to dominate the Danubian region. The Heruli kingdom known from later probably already existed in some form within Attila's empire, as did the kingdoms of the Ostrogoths, Scirii, and Gepids.