Battle of the Ries

King Louis the German surprised and routed the army of Count Adalbert of Metz on the banks of the river Wörnitz in the Ries.

The victory allowed Louis to join up with King Charles the Bald and defeat Lothar in the battle of Fontenoy-en-Puisaye in late June.

He stationed a large army in Alemannia to block the Roman roads and prevent Louis from joining up with Charles the Bald.

[8] Louis would have crossed the Danube and headed north on the left (east) bank of the Wörnitz, effectively leaving three major rivers between himself and Adalbert.

[2][8] Learning of Louis's movements, Adalbert must have crossed the Danube and headed north on the opposite bank of the Wörnitz.

Louis's intention was probably to force Adalbert to break up his army in many separate crossings, leaving him vulnerable to an ambush.

If this refers to the other side of the Wörnitz relative to Salzburg, where the annals were written, then it would seem that Louis crossed the river to surprise Adalbert.

On 25 June, they defeated the combined armies of Lothar and King Pippin II of Aquitaine in the battle of Fontenoy.