The Guglers were a body of mostly English and French knights who as mercenaries invaded Alsace and the Swiss plateau under the leadership of Enguerrand VII de Coucy during the Gugler War of 1375.
The Bernese attack on Fraubrunnen Abbey, from the Spiezer Chronik (1485). The Guglers, recognizable by their hooded helmets, had entrenched themselves in the abbey. Bernese troops summoned to reinforce the local population defeated the Guglers and set fire to the abbey, which suffered great damage as a result.
Chateau of Coucy showing donjon tower, watercolor, ca 1820 (Bibliothèque Nationale, Paris)