The Battle of Vlaardingen 1018

In the year 1018, the German emperor sent a military expedition towards Holland to subdue the rebellious Count Dirk III. Against all expectations, the large imperial army was defeated by the Vlaardingers and fled in panic.

Count Dirk had occupied peat lands that belonged to the bishop of Utrecht, and he levied toll from merchants who sailed by his stronghold along the river Merwede, between England and the port of Tiel. Both the bishop and the merchants complained to Emperor Henry II, who commanded a punitive expedition. He appointed Duke Godfrey of Lower-Lothringia as commander-in-chief. Godfrey assembled 1000 or maybe even 3000 experienced warriors from the bishoprics of Utrecht, Liege, Cologne and Cambrai and sailed towards Vlaardingen. After the fleet had landed on the bank of the river Merwede, the army marched towards Dirks stronghold. However, on the swampy ground, criss-crossed with ditches, they could not approach their goal directly, so the duke decided to make an outflanking movement. During this manoeuvre, Dirks men suddenly attacked him, from an ambush. In the rear guard of Godfreys army someone spread the rumour that the duke had fled the scene, upon which a panic broke out and everyone hurried back to the ships. The Vlaardingers, armed with swords and javelins, pursued the fleeing soldiers and killed almost all of them. Duke Godfrey himself did not flee, but bravely fought on. He narrowly survived, thanks to Count Dirk, who rescued him. The count made Godfrey promise that he would be left alone, so he could keep the occupied lands and could carry his business on. Under the rule of Dirk III and his successors, Holland developed into an independent and prosperous county.

More details and sources about The Battle of Vlaardingen can be found at
https://en.wikipedia.org/wiki/Battle_of_Vlaardingen and
http://www.keesn.nl/vlaard/vlaard_en.htm