how did gaius marius transform the roman military? group of answer choices by permitting landless men to serve in the army, he tapped a large reservoir of idle manpower. he developed a professional corps of engineers assigned to each legion to provide onsite advice and solutions to situations that arose. by permitting slaves to serve in the army with possibilities of freedom for service, he expanded the size of military forces dramatically. he established uniform military laws to which both officers and common soldiers were subject, which also gave them significant privileges for their service.