In November 1573, Fadrique laid siege to Leiden. Spanish troops meanwhile defeated a mercenary force led by Orange's brothers Louis and Henry of Nassau-Dillenburg in the Mookerheyde. In May 1574, the polders surrounding Leiden were flooded and a Sea Beggar fleet managed to lift the siege on 2 October 1574. Alba was replaced as regent by Requesens. In the summer of 1575, Requesens ordered Cristobal de Mondragon to attack the Zeeland city of Zierikzee, which surrendered on 2 July 1576; however, the Spanish troops mutinied and left Zierikzee. Philip had not been able to pay his troops for two years.