The Battle of Wlndr was fought in 934 between the allied Hungarian-Pecheneg army and an army composing of the forces of the Byzantine Empire and First Bulgarian Empire, somewhere in the territory which belonged to the Bulgarian empire, near a large city called W.l.n.d.r (perhaps Belgrade), by the Arab historian and geographer Al-Masudi. The battle resulted in a great victory for the Hungarian-Pecheneg forces, which they followed with a devastating raid up to the walls of Constantinople, forcing the Byzantine Empire to pay them tribute for many years (until 957). Al-Masudi's account of the battle is "one of the greatest descriptions of the nomadic war tactics."

Al-Masudi narrates an account of the battle and its causes in the 17th chapter of Vol. 2. of his work The Meadows of Gold, which is about the Caucasus and the countries and tribes which lived in it or north from it. In addition, the Byzantine chronicler Symeon the Metaphrast provides detailed information about the end of this campaign and the peace concluded between the Hungarian–Pecheneg alliance and the Byzantines.

In an academic work published in 1903, German historian Josef Marquart became the first scholar who considered the narrative from The Meadows of Gold to refer to the same events mentioned in the continuation of George Hamartolos' chronicle (Georgius Monachus Continuatus).

Al-Masudi is the only source that writes about the battle. His information about the location of the battle and the participants is a little confused. First, there is confusion about the place designated by the name W.l.n.d.r. Second, it is unclear precisely who participated in the battle on the side opposing the Byzantines, and how numerous they were. There are also questions about the Pecheneg involvement in the battle, and their number of troops.

Al-Masudi, as an Arab, wrote in the Arabic alphabet, which does not use letters for short vowels (although there are special diacritics for short vowels, called ḥarakāt, but they are not generally used, and they were not used by Al-Masudi). As a result, when he wrote down names of foreign tribes, towns and countries, it is hard to know how these names sounded, because only consonants are known. This is the case with ولندر = W.l.n.d.r (و - W, ل - l, ن - n, د - d, ر - r). In the translated editions of his work, Latin transcriptions of W.l.n.d.r appear with vowels chosen by the editors (Walendar in the French translation of Barbier de Meynard and Pavet de Courteille from 1838, Valandar or Vanandar in the Turkish edition from 2004), in order to make it easier to pronounce. The Hungarian translation of the part of al-Masudi's work which refers to the battle, writes the name correctly, putting points in the place of the vowels (ex. W.l.n.d.r).

Al-Masudi wrote his accounts about northern countries based on verbal information from people who visited these regions. As a result, some of his information has to be handled with care. For example, he writes that W.l.n.d.r was a Greek town between the mountains and the sea, but historians such as György Györffy and Gyula Kristó – accepting the claim of Josef Marquart – believe that it was not a city but a derivation of the old name of the Bulgarians: Onogur/Onogundur (Ten Oghur Tribes), which sounded *wn^ondur, which in old Hungarian became nándor, from which the old Hungarian name of Belgrade, Nándorfehérvár (White castle of the Bulgarians) originates, and in the works of the Arab geographer Ahmad ibn Rustah and the Persian geographer Abu Saʿīd Gardēzī, appears as W.n.n.d.r. So the historians conclude that W.l.n.d.r in reality was not a town, like al-Masudi believed, but the old name of the Bulgarians, so the battle was somewhere in the territory of the First Bulgarian Empire. Therefore, the battle was not fought around a town between the Byzantines and the Hungarian-Pecheneg army, but rather it was a battle between the Bulgarian Empire and the Byzantines against the Magyars and Pechenegs.

It is possible that the exact location of the battle was Belgrade, as orientalist Mihály Kmoskó considered, due to the fact that its old Hungarian name has in it the old, Turkic name of the Bulgarians in the form used by the Hungarians: nándor, and although is not near to a sea, but it is on the Danube's bank, which could be understood as sea, plus the Carpathian Mountains and Dinaric Alps are also close, and the mountain of Avala, and it was on the Hungarian border, so for its inhabitants would have been easy to attack their territories, as al-Masudi wrote. So in al-Masudi's text W.l.n.d.r could designate both the Bulgarians and the city of Belgrade, in some sentences designating the country, while others the city. But these are only suppositions. Josef Marquart identified the settlement with the fort Develtos laid near Burgas. Hansgerd Göckenjan and István Zimonyi considered Bulgarophygon (Babaeski) as the place of battle, based on the data that the relief army reached the besieged city in eight days from Constantinople.

Al-Masudi writes about four Turkic nations (a term designate the nomadic culture and lifestyle), who took part in the battle against the Byzantines: