The Arumer Zwarte Hoop, meaning "Black Heap of Arum" (West Frisian: Swarte Heap) was an army of peasant rebels and mercenaries in Friesland fighting against the Habsburg authorities from 1515 to 1523. For 4 years they were successful under the former farmer Pier Gerlofs Donia. Led by his Lieutenant Wijerd Jelckama from 1519 they slowly lost ground and were captured and executed in 1523.
The leader was the farmer Pier Gerlofs Donia, whose farm had been burned down and whose kinfolk had been killed by a marauding landsknecht regiment. Since the regiment had been employed by the Habsburg authorities to suppress the civil war of the Vetkopers and Schieringers, Donia put the blame on these authorities. After this he gathered angry peasants and some petty noblemen from Frisia and Gelderland and formed the Arumer Zwarte Hoop.
Under the leadership of Donia (nicknamed Greate Pier for his size), they employed guerrilla tactics and achieved several victories such as the successful siege of two Hollandic castles and the city of Medemblik. Donia also targeted ships that travelled the Zuiderzee and was very active in 1517, when he used his "signal ships" to attack ships in the region of the West Frisian coast, to which he also transported Geldrian forces, from the Duthcy of Geldern, setting them ashore at Medemblik. Donia bore a personal enmity to Medemblik and its inhabitants as, in earlier years, soldiers from Medemblik had cooperated with the Dutch army commanded by Duke Charles, the future Emperor. Donia sank 28 Dutch ships, earning him the title "Cross of the Dutchmen".
The rebels also received financial support from Charles II, Duke of Guelders, who claimed the Duchy of Guelders in opposition to the House of Habsburg. Charles also employed mercenaries under the command of Maarten van Rossum in their support. However, when the tides turned against the rebels after 1520, Charles withdrew his support. Losing their financial support, the rebels could then no longer afford to pay their mercenary army. About the same time, the Arumer Zwarte Hoop also lost their leader. In 1519, Donia's health deteriorated. He retired to his farm where he died in 1520. He is buried in Sneek in the 15th-century Groote Kerk (English: Large Church; also called the Martinikerk).