Sentence:  The besieged sprung a Mine under the Assailants first line, which buried Captain "Kalkreiter," and some Souldiers. But seeing they could not <WSD>take post</WSD> for want of Earth ... it was thought expedient to make a retreat; 
Meaning of the word marked with <WSD> tags:  To arrive in and occupy a position (somewhere), often a military one; to establish or station oneself in a (defensive or offensive) position.