In 1616 the Venetians besieged Farra and Gradisca, and the archduke attacked from Gorizia and Lucinico. With three large culverins, four guns and three small culverins, Farra  repulsed the enemy artillery with heavy losses. The Venetians launched another futile assault before Giustiniani lifted the siege and retreated to Mariano. In September, Johan Ernst van Nassau-Siegen agreed to raise 3,000 men from the Dutch Republic for Venetian service. They arrived in May 1617, followed six months later by another 2,000 . Spanish support was blocked at sea by a flotilla of 12 Dutch and 10 English warships and on land by the war in Mantua. Although Archduke Ferdinand had only 4,000 soldiers to defend Gradisca, he received military, political and financial support from the Spanish as part of a larger agreement: Philip agreed to fight the Venetians and support Ferdinand as the next Holy Roman Emperor in return for the cession of Alsace, Finale Ligure and Piombino. This led to a negotiated settlement between Ferdinand and the Venetians in which many Uskok pirates were executed or exiled, and a permanent Austrian garrison was installed in Senj.

Based on the above article, answer a question. What happend in May 1617?
Johan Ernst van Nassau-Siegen agreed