Sentence:  The construction of advanced <WSD>batteries</WSD> mirrored that of those built along the line of circumvallation. [...] Although Mahan demanded that <WSD>batteries</WSD> be constructed to exacting dimensions and revetted with gabions, fascines, and sandbags, at Vicksburg the resources at hand determined what materials soldiers used to build what they termed artillery "forts". 
Meaning of the word marked with <WSD> tags:  An elevated platform on which cannon could be placed.