Complex sentence: General Maroto continued defending his emplacement around Bilbao as he could and pleaded for artillery and reinforcements that never arrived but, on the contrary, two battalions were separated from his command and sent to the lines at San Sebastián.
Split into simpler sentences: General Maroto continued defending his encampment around Bilbao as well as he could while pleading for artillery and reinforcements that never arrived. In fact, two battalions were separated from his command and sent to the lines at San Sebastián.