Finally, in 1632, Frederick Henry was allowed to deliver his death blow. The initial move in his offensive was to have a reluctant States General publish (over the objections of the radical Calvinists) a proclamation promising that the free exercise of the Catholic religion would be guaranteed in places that the Dutch army would conquer that year. The inhabitants of the Southern Netherlands were invited to "throw off the yoke of the Spaniards". This piece of propaganda would prove to be very effective. Frederick Henry now invaded the Meuse valley with 30,000 troops. He took Venlo, Roermond, and Sittard in short order. As promised, the Catholic churches and clergy were left unmolested. Then, on 8 June, he laid siege to Maastricht. A desperate effort of Spanish and Imperialist forces to relieve the city failed and on 20 August 1632, Frederick Henry sprang his mines, breaching the walls of the city. It capitulated three days later. Here also, the Catholic religion was allowed to remain.