The Battle of Cologne was fought near the city of Köln (English: Cologne) (now part of Germany) in the year 716. The battle is known chiefly as the first battle of Charles Martel's command and is the only defeat of his life.
Outside of Cologne, the ultimate target of the invading army, held still by Plectrude, an ill-prepared Charles Martel, who had little time to gather many men, was defeated and forced to flee to the mountains of the Eifel. Martel had only recently been freed from imprisonment by Plectrude after his father's death, and most of his followers had not gathered. Faced with overwhelming numbers, lack of his own men, and no time to prepare, Charles chose to do the only thing he could: flee until he could gather his supporters and prepare. In short, Charles declined to give battle when he could not possibly win. Cologne then fell after a short siege to the king and the Neustrians.
But once in the mountains of the Eifel, Charles began to rally his supporters, and in short order was ready to do battle. He fell on the army of Chilperic II, and at the Battle of Amblève near Ameland Ragenfrid as they returned triumphantly from Cologne, and crushed their army. He used a feigned retreat, among other tactics for which he would become famous, primarily, attacking his foes when they least expected it, usually outnumbered, and depending on his generalship—in this case falling on his foes as they rested at midday, feigning retreat to draw them out of their defensive position, and crushing them in the open. He remained undefeated thereafter for twenty-five years, against a wide variety of foes, foreign and domestic, including his legendary defeat of the Muslim invasion of Europe at the Battle of Tours.