Complex sentence: The Spanish vanguard crossed a strategic bridge over the Teatinos River and took attack positions there, meanwhile the full force of the Patriot army at command of Santander had reached Casa de Piedra.
Split into simpler sentences: The Spanish vanguard crossed a strategic bridge over the Teatinos River and took attack positions there. Meanwhile, the full force of the Patriot army under Santander had reached Casa de Piedra.