The Battle of Oosterweel took place on March 13, 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, as lord of the city, was bound by oath to support the Spanish King.