With the arrival of large numbers of troops from Spain, Farnese began a campaign of reconquest in the south. He took advantage of the divisions in the ranks of his opponents between the Dutch-speaking Flemish and the French-speaking Walloons to foment growing discord. By doing so he was able to bring back the Walloon provinces to an allegiance to the king. By the treaty of Arras in 1579, he secured the support of the "Malcontents", as the Catholic nobles of the south were styled. The seven northern provinces, controlled by Calvinists, responded with the Union of Utrecht, where they resolved to stick together to fight Spain. Farnese secured his base in Hainaut and Artois, then moved against Brabant and Flanders. He captured many rebel towns in the south: Maastricht (1579), Tournai (1581), Oudenaarde (1582), Dunkirk (1583), Bruges (1584), and Ghent (1584). On August 17, 1585, Farnese laid siege to the great seaport of Antwerp.