Sentence:  ... Remember, sir, my liege, / The kings your ancestors, together with / The natural bravery of your isle, which stands / As Neptune's park, ribbed and paled in / With rocks <WSD>unscalable</WSD> and roaring waters, / With sands that will not bear your enemies' boats, / But suck them up to the topmast. ... 
Meaning of the word marked with <WSD> tags:  Not scalable, that cannot be climbed.