Sentence:  The Fort on the Mount St. "Catherine" after a Month's Siege was reduc'd to ſuch <WSD>Extremitys</WSD>, that they who defended it were forc'd to treat about a Surrender: and "Aug." 29. 'twas agreed between the "Engliſh" Commiſſioners, "Edward" Earl of "Mortaigne", w:Thomas Montagu, 4th Earl of Salisbury 
Meaning of the word marked with <WSD> tags:  An extreme measure.