At the commencement of the siege the citizens gathered all their food into the magazines, and at the end of June the daily allowance to each full grown man was half a pound of meat and half a pound of bread, women and children receiving less.

The prince had his headquarters at Delft and Rotterdam, and an important fortress called the Polderwaert between these two cities secured him the control of the district watered by the rivers Yssel and Maas. On the 29th of June the Spaniards attacked this fort, but were beaten off with a loss of 700 men. The prince was now occupied in endeavouring to persuade the Dutch authorities to permit the great sluices at Rotterdam, Schiedam, and Delft Haven to be opened. The damage to the country would be enormous; but there was no other course to rescue Leyden, and with it the whole of Holland, from destruction.

It was not until the middle of July that his eloquent appeals and arguments prevailed, and the estates consented to his plan. Subscriptions were opened in all the Dutch towns for maintaining the inhabitants of the district that was to be submerged until it could be again restored, and a large sum was raised, the women contributing their plate and jewellery to the furtherance of the scheme. On the 3rd of August all was ready, and the prince himself superintended the breaking down of the dykes in sixteen places, while at the same time the sluices at Schiedam and Rotterdam were opened and the water began to pour over the land.