William was the margrave (comes terminalis, "frontier count") of the March of Pannonia

March of Pannonia

The March of Pannonia was a frontier march of the Carolingian Empire erected in the mid-ninth century against the threat of Great Moravia and lasting only as long as the strength of that state....

 in the mid ninth century until his death on campaign against the Moravians

Moravians (ethnic group)

Moravians are the modern West Slavic inhabitants of the historical land of Moravia, the easternmost part of the Czech Republic, which includes the Moravian Slovakia. They speak the two main groups of Moravian dialects , the transitional Bohemian-Moravian dialect subgroup and standard Czech...

 in 871. In his day, the march orientalis corresponded to a front along the Danube

Danube

The Danube is a river in the Central Europe and the Europe's second longest river after the Volga. It is classified as an international waterway....

 from the Traun

Traun

Traun is a city in the state of Upper Austria, Austria. As of 2001, according to , the population was 23,470 . Traun is home to a large Turkish immigrant community, a significant part of which originates from Sakarya/Akyazi, Turkey. The city is located at latitude 48.21667, longitude...

gau to Szombathely

Szombathely

Szombathely is the 10th largest city in Hungary. It is the administrative centre of Vas county in the west of the country, located near the border with Austria...

 and the Rába

Rába

The Rába is a river in southeastern Austria and western Hungary and a right tributary of the Danube. Its source is in Austria, some kilometres east of Bruck an der Mur below Heubodenhöhe Hill. It flows through the Austrian states of Styria and Burgenland, and the Hungarian counties of Vas and...

 river and including the Vienna

Vienna

Vienna is the capital and largest city of the Republic of Austria and one of the nine states of Austria. Vienna is Austria's primary city, with a population of about 1.723 million , and is by far the largest city in Austria, as well as its cultural, economic, and political centre...

 basin. It was a military frontier zone against Avaria.

William co-ruled the march with his brother Engelschalk I

Engelschalk I

Engelschalk I was the margrave of the March of Pannonia in the mid ninth century until his death on campaign against the Moravians in 871. In his day, the march orientalis corresponded to a front along the Danube from the Traungau to the Szombathely and Raba rivers and including the Vienna basin...

 and both died on the same campaign. They were replaced by Aribo

Aribo of Austria

Aribo was the margrave of the March of Pannonia, from 871 until his death...

, but Engelschalk's son Engelschalk II

Engelschalk II

Engelschalk II was the margrave of the March of Pannonia in the late ninth century in opposition to Aribo...

 led their heirs in rebellion against Aribo in what became known as the Wilhelminer War

Wilhelminer War

Wilhelminer War was a minor war fought in the March of Pannonia from 882 to 884. It was initially a rebellion of the sons of the margraves William II and Engelschalk I, led by Engelschalk II, against the new margrave Aribo. Svatopluk I of Great Moravia intervened as an ally of Aribo because he had...

from 882 to 884. The "Wilhelminers" were descendants of William's father, William I.

Sources

• MacLean, Simon. Kingship and Politics in the Late Ninth Century: Charles the Fat and the end of the Carolingian Empire. Cambridge University Press: 2003.