This was a formidable obstacle, but the Spaniards, adept at land fighting and not amphibious warfare, had despaired of maintaining so unequal a contest against the combined forces of the sea and the veteran Dutch seamen. Accordingly, the Spanish commander Valdez ordered a retreat in the night of October 2, and the army fled, rendered more fearful by a terrible crash they heard from the city, and assumed to be the men of Leiden breaking still another dam upon them. In fact, part of the wall of Leiden, eroded by the sea water, had fallen, leaving the city completely vulnerable to attack, had any chosen to remain.