During the third century, the roman army hired several professional foreign soldiers called
a. pirates
b. mercenaries
c. legionnaires
d. missionaries

The correct answer is: "mercenaries".

By definition, a mercenary was a type a soldier who was hired to participate on a conflict or to conduct certain specific tasks, but who was not part of the regular army or of any military force controlled by the goverment.

In the late Roman Empire, authorities found it difficul to raise soldiers from its citizens, so they contacted with barbarians to constitute its armies. Previously,  these were romanized

b. andrew

the answer is a, salt plain