The Battle of Oosterweel took place on 13 March 1567 and is traditionally seen as the beginning of the Eighty Years' War. The battle was fought near the village of Oosterweel, north of Antwerp. A Spanish professional army under General Beauvoir defeated an army of radical Calvinists rebels under Jan de Marnix. The prisoners were considered rebels and all were killed. Some 700-800 Protestants died. William the Silent, the Burggraaf of Antwerp, did not allow the Protestants of the city to come to their aid, because he was, as lord of the city, bound by oath to support the Spanish King.
The battle and its aftermath are depicted in Cecelia Holland's novel The Sea Beggars - seen through the eyes of an idealistic young Calvinist from Antwerp who tries to join the rebels but (fortunately for him) arrives too late, to see them being overrun and killed by the Spanish cavalry.
Battle of Oosterweel. Banner with text "Vivent les Gueux". From Famiano Strada: Histoire de la guerre des Païs-Bas, 1727.